From 6450d2c318c6fca001bd9821747aed88f580d185 Mon Sep 17 00:00:00 2001
From: Kyrylo Simonov <xi@resolvent.net>
Date: Wed, 19 Feb 2025 09:33:51 -0600
Subject: [PATCH 1/5] Separate as() and into()

---
 src/FunSQL.jl         |   1 +
 src/link.jl           | 139 +++++++++++++++++++++---------------------
 src/nodes.jl          |   1 +
 src/nodes/as.jl       |  17 +++---
 src/nodes/hide.jl     |  42 +++++++++++++
 src/nodes/internal.jl |  20 ++----
 src/nodes/into.jl     |  28 +++++++++
 src/resolve.jl        |  34 +++++------
 src/translate.jl      |  66 ++++++++------------
 9 files changed, 196 insertions(+), 152 deletions(-)
 create mode 100644 src/nodes/hide.jl
 create mode 100644 src/nodes/into.jl

diff --git a/src/FunSQL.jl b/src/FunSQL.jl
index fb6a5ca8..618c6610 100644
--- a/src/FunSQL.jl
+++ b/src/FunSQL.jl
@@ -56,6 +56,7 @@ export
     funsql_group,
     funsql_highlight,
     funsql_in,
+    funsql_into,
     funsql_iterate,
     funsql_is_not_null,
     funsql_is_null,
diff --git a/src/link.jl b/src/link.jl
index 00015f41..3736efea 100644
--- a/src/link.jl
+++ b/src/link.jl
@@ -123,19 +123,15 @@ function dismantle(n::GroupNode, ctx)
     Group(by = by′, sets = n.sets, name = n.name, label_map = n.label_map, tail = tail′)
 end
 
-function dismantle(n::IterateNode, ctx)
+function dismantle(n::IntoNode, ctx)
     tail′ = dismantle(ctx)
-    iterator′ = dismantle(n.iterator, ctx)
-    Iterate(iterator = iterator′, tail = tail′)
+    Into(name = n.name, tail = tail′)
 end
 
-function dismantle(n::JoinNode, ctx)
-    rt = row_type(n.joinee)
-    router = JoinRouter(Set(keys(rt.fields)), !isa(rt.group, EmptyType))
+function dismantle(n::IterateNode, ctx)
     tail′ = dismantle(ctx)
-    joinee′ = dismantle(n.joinee, ctx)
-    on′ = dismantle_scalar(n.on, ctx)
-    RoutedJoin(joinee = joinee′, on = on′, router = router, left = n.left, right = n.right, optional = n.optional, tail = tail′)
+    iterator′ = dismantle(n.iterator, ctx)
+    Iterate(iterator = iterator′, tail = tail′)
 end
 
 function dismantle(n::LimitNode, ctx)
@@ -181,6 +177,13 @@ function dismantle_scalar(n::ResolvedNode, ctx)
     end
 end
 
+function dismantle(n::RoutedJoinNode, ctx)
+    tail′ = dismantle(ctx)
+    joinee′ = dismantle(n.joinee, ctx)
+    on′ = dismantle_scalar(n.on, ctx)
+    RoutedJoin(joinee = joinee′, on = on′, name = n.name, left = n.left, right = n.right, optional = n.optional, tail = tail′)
+end
+
 function dismantle(n::SelectNode, ctx)
     tail′ = dismantle(ctx)
     args′ = dismantle_scalar(n.args, ctx)
@@ -232,16 +235,7 @@ function link(n::AppendNode, ctx)
 end
 
 function link(n::AsNode, ctx)
-    refs = SQLQuery[]
-    for ref in ctx.refs
-        if @dissect(ref, (local tail) |> Nested(name = (local name)))
-            @assert name == n.name
-            push!(refs, tail)
-        else
-            error()
-        end
-    end
-    tail′ = link(ctx.tail, ctx, refs)
+    tail′ = link(ctx)
     As(name = n.name, tail = tail′)
 end
 
@@ -289,10 +283,8 @@ function link(n::FromIterateNode, ctx)
 end
 
 function link(n::FromTableExpressionNode, ctx)
-    refs = ctx.cte_refs[(n.name, n.depth)]
-    for ref in ctx.refs
-        push!(refs, Nested(name = n.name, tail = ref))
-    end
+    cte_refs = ctx.cte_refs[(n.name, n.depth)]
+    append!(cte_refs, ctx.refs)
     n
 end
 
@@ -333,6 +325,20 @@ function link(n::GroupNode, ctx)
     Group(by = n.by, sets = n.sets, name = n.name, label_map = n.label_map, tail = tail′)
 end
 
+function link(n::IntoNode, ctx)
+    refs = SQLQuery[]
+    for ref in ctx.refs
+        if @dissect(ref, (local tail) |> Nested(name = (local name)))
+            @assert name == n.name
+            push!(refs, tail)
+        else
+            error()
+        end
+    end
+    tail′ = link(ctx.tail, ctx, refs)
+    Into(name = n.name, tail = tail′)
+end
+
 function link(n::IterateNode, ctx)
     iterator′ = n.iterator
     defs = copy(ctx.defs)
@@ -364,53 +370,6 @@ function link(n::IterateNode, ctx)
     Padding(tail = q′)
 end
 
-function route(r::JoinRouter, ref::SQLQuery)
-    if @dissect(ref, Nested(name = (local name))) && name in r.label_set
-        return 1
-    end
-    if @dissect(ref, Get(name = (local name))) && name in r.label_set
-        return 1
-    end
-    if @dissect(ref, Agg()) && r.group
-        return 1
-    end
-    return -1
-end
-
-function link(n::RoutedJoinNode, ctx)
-    lrefs = SQLQuery[]
-    rrefs = SQLQuery[]
-    for ref in ctx.refs
-        turn = route(n.router, ref)
-        push!(turn < 0 ? lrefs : rrefs, ref)
-    end
-    if n.optional && isempty(rrefs)
-        return link(ctx)
-    end
-    ln_ext_refs = length(lrefs)
-    rn_ext_refs = length(rrefs)
-    refs′ = SQLQuery[]
-    lateral_refs = SQLQuery[]
-    gather!(n.joinee, ctx, lateral_refs)
-    append!(lrefs, lateral_refs)
-    lateral = !isempty(lateral_refs)
-    gather!(n.on, ctx, refs′)
-    for ref in refs′
-        turn = route(n.router, ref)
-        push!(turn < 0 ? lrefs : rrefs, ref)
-    end
-    tail′ = Linked(lrefs, ln_ext_refs, tail = link(ctx.tail, ctx, lrefs))
-    joinee′ = Linked(rrefs, rn_ext_refs, tail = link(n.joinee, ctx, rrefs))
-    RoutedJoin(
-        joinee = joinee′,
-        on = n.on,
-        router = n.router,
-        left = n.left,
-        right = n.right,
-        lateral = lateral,
-        tail = tail′)
-end
-
 function link(n::LimitNode, ctx)
     tail′ = Linked(ctx.refs, tail = link(ctx))
     Limit(offset = n.offset, limit = n.limit, tail = tail′)
@@ -459,6 +418,46 @@ function link(n::PartitionNode, ctx)
     Partition(by = n.by, order_by = n.order_by, frame = n.frame, name = n.name, tail = tail′)
 end
 
+function link(n::RoutedJoinNode, ctx)
+    lrefs = SQLQuery[]
+    rrefs = SQLQuery[]
+    for ref in ctx.refs
+        if @dissect(ref, Nested(name = (local name))) && name === n.name
+            push!(rrefs, ref)
+        else
+            push!(lrefs, ref)
+        end
+    end
+    if n.optional && isempty(rrefs)
+        return link(ctx)
+    end
+    ln_ext_refs = length(lrefs)
+    rn_ext_refs = length(rrefs)
+    refs′ = SQLQuery[]
+    lateral_refs = SQLQuery[]
+    gather!(n.joinee, ctx, lateral_refs)
+    append!(lrefs, lateral_refs)
+    lateral = !isempty(lateral_refs)
+    gather!(n.on, ctx, refs′)
+    for ref in refs′
+        if @dissect(ref, Nested(name = (local name))) && name === n.name
+            push!(rrefs, ref)
+        else
+            push!(lrefs, ref)
+        end
+    end
+    tail′ = Linked(lrefs, ln_ext_refs, tail = link(ctx.tail, ctx, lrefs))
+    joinee′ = Linked(rrefs, rn_ext_refs, tail = link(Into(name = n.name, tail = n.joinee), ctx, rrefs))
+    RoutedJoin(
+        joinee = joinee′,
+        on = n.on,
+        name = n.name,
+        left = n.left,
+        right = n.right,
+        lateral = lateral,
+        tail = tail′)
+end
+
 function link(n::SelectNode, ctx)
     refs = SQLQuery[]
     gather!(n.args, ctx, refs)
diff --git a/src/nodes.jl b/src/nodes.jl
index ab470726..5fc547c0 100644
--- a/src/nodes.jl
+++ b/src/nodes.jl
@@ -913,6 +913,7 @@ include("nodes/get.jl")
 include("nodes/group.jl")
 include("nodes/highlight.jl")
 include("nodes/internal.jl")
+include("nodes/into.jl")
 include("nodes/iterate.jl")
 include("nodes/join.jl")
 include("nodes/limit.jl")
diff --git a/src/nodes/as.jl b/src/nodes/as.jl
index 3a4a5db7..d1a61a2d 100644
--- a/src/nodes/as.jl
+++ b/src/nodes/as.jl
@@ -16,8 +16,7 @@ AsNode(name) =
     As(name; tail = nothing)
     name => tail
 
-In a scalar context, `As` specifies the name of the output column.  When
-applied to tabular data, `As` wraps the data in a nested record.
+`As` specifies the name of the output column.
 
 The arrow operator (`=>`) is a shorthand notation for `As`.
 
@@ -35,19 +34,19 @@ SELECT "person_1"."person_id" AS "id"
 FROM "person" AS "person_1"
 ```
 
-*Show all patients together with their state of residence.*
+*Show all patients together with their primary care provider.*
 
 ```jldoctest
-julia> person = SQLTable(:person, columns = [:person_id, :year_of_birth, :location_id]);
+julia> person = SQLTable(:person, columns = [:person_id, :year_of_birth, :provider_id]);
 
-julia> location = SQLTable(:location, columns = [:location_id, :state]);
+julia> provider = SQLTable(:provider, columns = [:provider_id, :provider_name]);
 
 julia> q = From(:person) |>
-           Join(From(:location) |> As(:location),
-                on = Get.location_id .== Get.location.location_id) |>
-           Select(Get.person_id, Get.location.state);
+           Join(From(:provider) |> As(:pcp),
+                on = Get.provider_id .== Get.pcp.provider_id) |>
+           Select(Get.person_id, Get.pcp.provider_name);
 
-julia> print(render(q, tables = [person, location]))
+julia> print(render(q, tables = [person, provider]))
 SELECT
   "person_1"."person_id",
   "location_1"."state"
diff --git a/src/nodes/hide.jl b/src/nodes/hide.jl
new file mode 100644
index 00000000..36ced02c
--- /dev/null
+++ b/src/nodes/hide.jl
@@ -0,0 +1,42 @@
+# Hide node
+
+mutable struct HideNode <: TabularNode
+    over::Union{SQLNode, Nothing}
+    names::Vector{Symbol}
+    label_map::FunSQL.OrderedDict{Symbol, Int}
+
+    function HideNode(; over = nothing, names = [], label_map = nothing)
+        if label_map !== nothing
+            new(over, names, label_map)
+        else
+            n = new(over, names, FunSQL.OrderedDict{Symbol, Int}())
+            for (i, name) in enumerate(n.names)
+                if name in keys(n.label_map)
+                    err = FunSQL.DuplicateLabelError(name, path = [n])
+                    throw(err)
+                end
+                n.label_map[name] = i
+            end
+            n
+        end
+    end
+end
+
+HideNode(names...; over = nothing) =
+    HideNode(over = over, names = Symbol[names...])
+
+Hide(args...; kws...) =
+    HideNode(args...; kws...) |> SQLNode
+
+const funsql_hide = Hide
+
+dissect(scr::Symbol, ::typeof(Hide), pats::Vector{Any}) =
+    dissect(scr, HideNode, pats)
+
+function FunSQL.PrettyPrinting.quoteof(n::HideNode, ctx::FunSQL.QuoteContext)
+    ex = Expr(:call, nameof(Hide), quoteof(n.names, ctx)...)
+    if n.over !== nothing
+        ex = Expr(:call, :|>, FunSQL.quoteof(n.over, ctx), ex)
+    end
+    ex
+end
diff --git a/src/nodes/internal.jl b/src/nodes/internal.jl
index 91f866fd..931afb97 100644
--- a/src/nodes/internal.jl
+++ b/src/nodes/internal.jl
@@ -203,29 +203,21 @@ PrettyPrinting.quoteof(n::FromFunctionNode, ctx::QuoteContext) =
 
 
 # Annotated Join node.
-struct JoinRouter
-    label_set::Set{Symbol}
-    group::Bool
-end
-
-PrettyPrinting.quoteof(r::JoinRouter) =
-    Expr(:call, :JoinRouter, quoteof(r.label_set), quoteof(r.group))
-
 struct RoutedJoinNode <: TabularNode
     joinee::SQLQuery
     on::SQLQuery
-    router::JoinRouter
+    name::Symbol
     left::Bool
     right::Bool
     lateral::Bool
     optional::Bool
 
-    RoutedJoinNode(; joinee, on, router, left, right, lateral = false, optional = false) =
-        new(joinee, on, router, left, right, lateral, optional)
+    RoutedJoinNode(; joinee, on, name = label(joinee), left, right, lateral = false, optional = false) =
+        new(joinee, on, name, left, right, lateral, optional)
 end
 
-RoutedJoinNode(joinee, on; router, left = false, right = false, lateral = false, optional = false) =
-    RoutedJoinNode(joinee = joinee, on = on, router, left = left, right = right, lateral = lateral, optional = optional)
+RoutedJoinNode(joinee, on; name = label(joinee), left = false, right = false, lateral = false, optional = false) =
+    RoutedJoinNode(name = name, on = on, router, left = left, right = right, lateral = lateral, optional = optional)
 
 const RoutedJoin = SQLQueryCtor{RoutedJoinNode}(:RoutedJoin)
 
@@ -234,7 +226,7 @@ function PrettyPrinting.quoteof(n::RoutedJoinNode, ctx::QuoteContext)
     if !ctx.limit
         push!(ex.args, quoteof(n.joinee, ctx))
         push!(ex.args, quoteof(n.on, ctx))
-        push!(ex.args, Expr(:kw, :router, quoteof(n.router)))
+        push!(ex.args, Expr(:kw, :name, QuoteNode(n.name)))
         if n.left
             push!(ex.args, Expr(:kw, :left, n.left))
         end
diff --git a/src/nodes/into.jl b/src/nodes/into.jl
new file mode 100644
index 00000000..f421ea1e
--- /dev/null
+++ b/src/nodes/into.jl
@@ -0,0 +1,28 @@
+# Wrap the output into a nested record.
+
+mutable struct IntoNode <: TabularNode
+    name::Symbol
+
+    IntoNode(; name::Union{Symbol, AbstractString}) =
+        new(Symbol(name))
+end
+
+IntoNode(name) =
+    IntoNode(; name)
+
+"""
+    Into(; name, tail = nothing)
+    Into(name; tail = nothing)
+
+`Into` wraps output columns in a nested record.
+"""
+const Into = SQLQueryCtor{IntoNode}(:Into)
+
+const funsql_into = Into
+
+function PrettyPrinting.quoteof(n::IntoNode, ctx::QuoteContext)
+    Expr(:call, :Into, quoteof(n.name))
+end
+
+label(n::IntoNode) =
+    n.name
diff --git a/src/resolve.jl b/src/resolve.jl
index 73bf67ac..56136edb 100644
--- a/src/resolve.jl
+++ b/src/resolve.jl
@@ -178,9 +178,8 @@ end
 
 function resolve(n::AsNode, ctx)
     tail′ = resolve(ctx)
-    t = row_type(tail′)
     q′ = As(name = n.name, tail = tail′)
-    Resolved(RowType(FieldTypeMap(n.name => t)), tail = q′)
+    Resolved(type(tail′), tail = q′)
 end
 
 function resolve_scalar(n::AsNode, ctx)
@@ -401,6 +400,13 @@ resolve(::HighlightNode, ctx) =
 resolve_scalar(::HighlightNode, ctx) =
     resolve_scalar(ctx)
 
+function resolve(n::IntoNode, ctx)
+    tail′ = resolve(ctx)
+    t = row_type(tail′)
+    q′ = Into(name = n.name, tail = tail′)
+    Resolved(RowType(FieldTypeMap(n.name => t)), tail = q′)
+end
+
 function resolve(n::IterateNode, ctx)
     tail′ = resolve(ResolveContext(ctx, knot_type = nothing, implicit_knot = false))
     t = row_type(tail′)
@@ -418,21 +424,18 @@ end
 function resolve(n::JoinNode, ctx)
     tail′ = resolve(ctx)
     lt = row_type(tail′)
+    name = label(n.joinee)
     joinee′ = resolve(n.joinee, ResolveContext(ctx, row_type = lt, implicit_knot = false))
     rt = row_type(joinee′)
     fields = FieldTypeMap()
     for (f, ft) in lt.fields
-        fields[f] = get(rt.fields, f, ft)
+        fields[f] = ft
     end
-    for (f, ft) in rt.fields
-        if !haskey(fields, f)
-            fields[f] = ft
-        end
-    end
-    group = rt.group isa EmptyType ? lt.group : rt.group
+    fields[name] = rt
+    group = lt.group
     t = RowType(fields, group)
     on′ = resolve_scalar(n.on, ctx, t)
-    q′ = Join(joinee = joinee′, on = on′, left = n.left, right = n.right, optional = n.optional, tail = tail′)
+    q′ = RoutedJoin(joinee = joinee′, on = on′, name = name, left = n.left, right = n.right, optional = n.optional, tail = tail′)
     Resolved(t, tail = q′)
 end
 
@@ -532,16 +535,7 @@ function resolve(n::Union{WithNode, WithExternalNode}, ctx)
         v = get(ctx.cte_types, name, nothing)
         depth = 1 + (v !== nothing ? v[1] : 0)
         t = row_type(args′[i])
-        cte_t = get(t.fields, name, EmptyType())
-        if !(cte_t isa RowType)
-            throw(
-                ReferenceError(
-                    REFERENCE_ERROR_TYPE.INVALID_TABLE_REFERENCE,
-                    name = name,
-                    path = get_path(ctx)))
-
-        end
-        cte_types′ = Base.ImmutableDict(cte_types′, name => (depth, cte_t))
+        cte_types′ = Base.ImmutableDict(cte_types′, name => (depth, t))
     end
     ctx′ = ResolveContext(ctx, cte_types = cte_types′)
     tail′ = resolve(ctx′)
diff --git a/src/translate.jl b/src/translate.jl
index 84b3bd79..0e4a16fb 100644
--- a/src/translate.jl
+++ b/src/translate.jl
@@ -427,26 +427,8 @@ function assemble(n::AppendNode, ctx)
     Assemblage(a_name, s, repl = repl, cols = dummy_cols)
 end
 
-function assemble(n::AsNode, ctx)
-    refs′ = SQLQuery[]
-    for ref in ctx.refs
-        if @dissect(ref, (local tail) |> Nested())
-            push!(refs′, tail)
-        else
-            push!(refs′, ref)
-        end
-    end
-    base = assemble(TranslateContext(ctx, refs = refs′))
-    repl′ = Dict{SQLQuery, Symbol}()
-    for ref in ctx.refs
-        if @dissect(ref, (local tail) |> Nested())
-            repl′[ref] = base.repl[tail]
-        else
-            repl′[ref] = base.repl[ref]
-        end
-    end
-    Assemblage(n.name, base.syntax, cols = base.cols, repl = repl′)
-end
+assemble(n::AsNode, ctx) =
+    assemble(ctx)
 
 function assemble(n::BindNode, ctx)
     vars′ = ctx.vars
@@ -530,21 +512,12 @@ end
 assemble(::FromNothingNode, ctx) =
     assemble(nothing, ctx)
 
-function unwrap_repl(a::Assemblage)
-    repl′ = Dict{SQLQuery, Symbol}()
-    for (ref, name) in a.repl
-        @dissect(ref, (local tail) |> Nested()) || error()
-        repl′[tail] = name
-    end
-    Assemblage(a.name, a.syntax, cols = a.cols, repl = repl′)
-end
-
 function assemble(n::FromTableExpressionNode, ctx)
     cte_a = ctx.ctes[ctx.cte_map[(n.name, n.depth)]]
     alias = allocate_alias(ctx, n.name)
     tbl = convert(SQLSyntax, (cte_a.qualifiers, cte_a.name))
     s = FROM(AS(name = alias, tail = tbl))
-    subs = make_subs(unwrap_repl(cte_a.a), alias)
+    subs = make_subs(cte_a.a, alias)
     trns = Pair{SQLQuery, SQLSyntax}[]
     for ref in ctx.refs
         push!(trns, ref => subs[ref])
@@ -675,6 +648,27 @@ function assemble(n::GroupNode, ctx)
     return Assemblage(base.name, s, cols = cols, repl = repl)
 end
 
+function assemble(n::IntoNode, ctx)
+    refs′ = SQLQuery[]
+    for ref in ctx.refs
+        if @dissect(ref, (local tail) |> Nested())
+            push!(refs′, tail)
+        else
+            push!(refs′, ref)
+        end
+    end
+    base = assemble(TranslateContext(ctx, refs = refs′))
+    repl′ = Dict{SQLQuery, Symbol}()
+    for ref in ctx.refs
+        if @dissect(ref, (local tail) |> Nested())
+            repl′[ref] = base.repl[tail]
+        else
+            repl′[ref] = base.repl[ref]
+        end
+    end
+    Assemblage(n.name, base.syntax, cols = base.cols, repl = repl′)
+end
+
 function assemble(n::IterateNode, ctx)
     ctx′ = TranslateContext(ctx, vars = Base.ImmutableDict{Tuple{Symbol, Int}, SQLSyntax}())
     left = assemble(ctx)
@@ -883,22 +877,16 @@ function assemble(n::RoutedJoinNode, ctx)
         right = assemble(n.joinee, ctx)
     end
     if @dissect(right.syntax, (local joinee = (ID() || AS())) |> FROM()) && (!n.left || _outer_safe(right))
-        for (ref, name) in right.repl
-            subs[ref] = right.cols[name]
-        end
+        right_alias = nothing
         if ctx.catalog.dialect.has_implicit_lateral
             lateral = false
         end
     else
         right_alias = allocate_alias(ctx, right)
         joinee = AS(name = right_alias, tail = complete(right))
-        right_cache = Dict{Symbol, SQLSyntax}()
-        for (ref, name) in right.repl
-            subs[ref] = get(right_cache, name) do
-                ID(name = name, tail = right_alias)
-            end
-        end
     end
+    right_subs = make_subs(right, right_alias)
+    merge!(subs, right_subs)
     on = translate(n.on, ctx, subs)
     s = JOIN(joinee = joinee, on = on, left = n.left, right = n.right, lateral = lateral, tail = tail)
     trns = Pair{SQLQuery, SQLSyntax}[]

From a70eaff4d98242fafd7019d924bbf15362b96a4e Mon Sep 17 00:00:00 2001
From: Kyrylo Simonov <xi@resolvent.net>
Date: Wed, 19 Feb 2025 21:17:08 -0600
Subject: [PATCH 2/5] Make nested records visible

---
 src/link.jl | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/src/link.jl b/src/link.jl
index 3736efea..d79cdcbb 100644
--- a/src/link.jl
+++ b/src/link.jl
@@ -25,16 +25,26 @@ struct LinkContext
             knot_refs)
 end
 
-function link(q::SQLQuery)
-    @dissect(q, (local tail) |> WithContext(catalog = (local catalog))) || throw(IllFormedError())
-    ctx = LinkContext(catalog)
-    t = row_type(tail)
+function _select(t::RowType)
     refs = SQLQuery[]
     for (f, ft) in t.fields
         if ft isa ScalarType
             push!(refs, Get(f))
+        else
+            nested_refs = _select(ft)
+            for nested_ref in nested_refs
+                push!(refs, Nested(over = nested_ref, name = f))
+            end
         end
     end
+    refs
+end
+
+function link(q::SQLQuery)
+    @dissect(q, (local tail) |> WithContext(catalog = (local catalog))) || throw(IllFormedError())
+    ctx = LinkContext(catalog)
+    t = row_type(tail)
+    refs = _select(t)
     tail′ = Linked(refs, tail = link(dismantle(tail, ctx), ctx, refs))
     WithContext(tail = tail′, catalog = catalog, defs = ctx.defs)
 end
@@ -555,12 +565,9 @@ end
 function gather!(n::IsolatedNode, ctx)
     def = ctx.defs[n.idx]
     !@dissect(def, Linked()) || return
-    refs = SQLQuery[]
-    for (f, ft) in n.type.fields
-        if ft isa ScalarType
-            push!(refs, Get(f))
-            break
-        end
+    refs = _select(n.type)
+    if !isempty(refs)
+        refs = refs[1:1]
     end
     def′ = Linked(refs, tail = link(def, ctx, refs))
     ctx.defs[n.idx] = def′

From 8149fcfc8f5d41fc88e4baf5f7d6bd258f50e2ad Mon Sep 17 00:00:00 2001
From: Kyrylo Simonov <xi@resolvent.net>
Date: Sat, 22 Feb 2025 13:58:58 -0600
Subject: [PATCH 3/5] Join: add swap option

---
 src/nodes/join.jl | 25 ++++++++++++++++---------
 src/resolve.jl    |  4 ++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/src/nodes/join.jl b/src/nodes/join.jl
index c1bc2eb4..372d2272 100644
--- a/src/nodes/join.jl
+++ b/src/nodes/join.jl
@@ -6,21 +6,22 @@ mutable struct JoinNode <: TabularNode
     left::Bool
     right::Bool
     optional::Bool
+    swap::Bool
 
-    JoinNode(; joinee, on, left = false, right = false, optional = false) =
-        new(joinee, on, left, right, optional)
+    JoinNode(; joinee, on, left = false, right = false, optional = false, swap = false) =
+        new(joinee, on, left, right, optional, swap)
 end
 
-JoinNode(joinee; on, left = false, right = false, optional = false) =
-    JoinNode(; joinee, on, left, right, optional)
+JoinNode(joinee; on, left = false, right = false, optional = false, swap = false) =
+    JoinNode(; joinee, on, left, right, optional, swap)
 
-JoinNode(joinee, on; left = false, right = false, optional = false) =
-    JoinNode(; joinee, on, left, right, optional)
+JoinNode(joinee, on; left = false, right = false, optional = false, swap = false) =
+    JoinNode(; joinee, on, left, right, optional, swap)
 
 """
-    Join(; joinee, on, left = false, right = false, optional = false)
-    Join(joinee; on, left = false, right = false, optional = false)
-    Join(joinee, on; left = false, right = false, optional = false)
+    Join(; joinee, on, left = false, right = false, optional = false, swap = false)
+    Join(joinee; on, left = false, right = false, optional = false, swap = false)
+    Join(joinee, on; left = false, right = false, optional = false, swap = false)
 
 `Join` correlates two input datasets.
 
@@ -102,8 +103,14 @@ function PrettyPrinting.quoteof(n::JoinNode, ctx::QuoteContext)
         if n.optional
             push!(ex.args, Expr(:kw, :optional, n.optional))
         end
+        if n.swap
+            push!(ex.args, Expr(:kw, :swap, n.swap))
+        end
     else
         push!(ex.args, :…)
     end
     ex
 end
+
+label(n::JoinNode) =
+    n.swap ? label(n.joinee) : label(n.over)
diff --git a/src/resolve.jl b/src/resolve.jl
index 56136edb..bcdb6e21 100644
--- a/src/resolve.jl
+++ b/src/resolve.jl
@@ -422,6 +422,10 @@ function resolve(n::IterateNode, ctx)
 end
 
 function resolve(n::JoinNode, ctx)
+    if n.swap
+        ctx′ = ResolveContext(Ctx, tail = n.joinee)
+        return resolve(JoinNode(joinee = ctx.tail, on = n.on, left = n.right, right = n.left, optional = n.optional), ctx′)
+    end
     tail′ = resolve(ctx)
     lt = row_type(tail′)
     name = label(n.joinee)

From 9edf1591e044a7b2e3ca76074b2207d209ec9a11 Mon Sep 17 00:00:00 2001
From: Kyrylo Simonov <xi@resolvent.net>
Date: Sat, 22 Feb 2025 17:18:45 -0600
Subject: [PATCH 4/5] Add Show/Hide combinators

---
 src/FunSQL.jl         |  2 ++
 src/link.jl           |  4 +++-
 src/nodes.jl          | 15 +++++++++------
 src/nodes/internal.jl |  2 +-
 src/nodes/show.jl     | 38 ++++++++++++++++++++++++++++++++++++++
 src/resolve.jl        | 29 ++++++++++++++++++++++++++++-
 src/types.jl          | 30 +++++++++++++++++++++++-------
 7 files changed, 104 insertions(+), 16 deletions(-)
 create mode 100644 src/nodes/show.jl

diff --git a/src/FunSQL.jl b/src/FunSQL.jl
index 618c6610..56e4378a 100644
--- a/src/FunSQL.jl
+++ b/src/FunSQL.jl
@@ -54,6 +54,7 @@ export
     funsql_from,
     funsql_fun,
     funsql_group,
+    funsql_hide,
     funsql_highlight,
     funsql_in,
     funsql_into,
@@ -83,6 +84,7 @@ export
     funsql_rank,
     funsql_row_number,
     funsql_select,
+    funsql_show,
     funsql_sort,
     funsql_sum,
     funsql_with
diff --git a/src/link.jl b/src/link.jl
index d79cdcbb..c9eada38 100644
--- a/src/link.jl
+++ b/src/link.jl
@@ -27,13 +27,15 @@ end
 
 function _select(t::RowType)
     refs = SQLQuery[]
+    t.visible || return refs
     for (f, ft) in t.fields
         if ft isa ScalarType
+            ft.visible || continue
             push!(refs, Get(f))
         else
             nested_refs = _select(ft)
             for nested_ref in nested_refs
-                push!(refs, Nested(over = nested_ref, name = f))
+                push!(refs, Nested(name = f, tail = nested_ref))
             end
         end
     end
diff --git a/src/nodes.jl b/src/nodes.jl
index 5fc547c0..e16e70ef 100644
--- a/src/nodes.jl
+++ b/src/nodes.jl
@@ -54,17 +54,19 @@ terminal(q::SQLQuery) =
 Chain(q′, q) =
     convert(SQLQuery, q)(q′)
 
-label(q::SQLQuery) =
-    @something label(q.head) label(q.tail)
+function label(q::SQLQuery; default = :_)
+    l = label(q.head)
+    l !== nothing ? l : label(q.tail; default)
+end
 
 label(n::AbstractSQLNode) =
     nothing
 
-label(::Nothing) =
-    :_
+label(::Nothing; default = :_) =
+    default
 
-label(q) =
-    label(convert(SQLQuery, q))
+label(q; default = :_) =
+    label(convert(SQLQuery, q); default)
 
 
 # A variant of SQLQuery for assembling a chain of identifiers.
@@ -922,6 +924,7 @@ include("nodes/order.jl")
 include("nodes/over.jl")
 include("nodes/partition.jl")
 include("nodes/select.jl")
+include("nodes/show.jl")
 include("nodes/sort.jl")
 include("nodes/variable.jl")
 include("nodes/where.jl")
diff --git a/src/nodes/internal.jl b/src/nodes/internal.jl
index 931afb97..36221e3e 100644
--- a/src/nodes/internal.jl
+++ b/src/nodes/internal.jl
@@ -302,7 +302,7 @@ PrettyPrinting.quoteof(n::FunSQLMacroNode, ctx::QuoteContext) =
     Expr(:macrocall, Symbol("@funsql"), n.line, !ctx.limit ? n.ex : :…)
 
 label(n::FunSQLMacroNode) =
-    label(n.query)
+    label(n.query, default = nothing)
 
 
 # Unwrap @funsql macro when displaying the query.
diff --git a/src/nodes/show.jl b/src/nodes/show.jl
new file mode 100644
index 00000000..f0176ec7
--- /dev/null
+++ b/src/nodes/show.jl
@@ -0,0 +1,38 @@
+# Show/Hide nodes
+
+mutable struct ShowNode <: TabularNode
+    names::Vector{Symbol}
+    visible::Bool
+    label_map::FunSQL.OrderedDict{Symbol, Int}
+
+    function ShowNode(; names = [], visible = true, label_map = nothing)
+        if label_map !== nothing
+            new(names, visible, label_map)
+        else
+            n = new(names, visible, FunSQL.OrderedDict{Symbol, Int}())
+            for (i, name) in enumerate(n.names)
+                if name in keys(n.label_map)
+                    err = FunSQL.DuplicateLabelError(name, path = SQLQuery[n])
+                    throw(err)
+                end
+                n.label_map[name] = i
+            end
+            n
+        end
+    end
+end
+
+ShowNode(names...; visible = true) =
+    ShowNode(names = Symbol[names...], visible = visible)
+
+const Show = SQLQueryCtor{ShowNode}(:Show)
+
+Hide(args...; kws...) =
+    Show(args...; kws..., visible = false)
+
+const funsql_show = Show
+const funsql_hide = Hide
+
+function FunSQL.PrettyPrinting.quoteof(n::ShowNode, ctx::QuoteContext)
+    Expr(:call, n.visible ? :Show : :Hide, quoteof(n.names, ctx)...)
+end
diff --git a/src/resolve.jl b/src/resolve.jl
index bcdb6e21..1e901673 100644
--- a/src/resolve.jl
+++ b/src/resolve.jl
@@ -423,7 +423,7 @@ end
 
 function resolve(n::JoinNode, ctx)
     if n.swap
-        ctx′ = ResolveContext(Ctx, tail = n.joinee)
+        ctx′ = ResolveContext(ctx, tail = n.joinee)
         return resolve(JoinNode(joinee = ctx.tail, on = n.on, left = n.right, right = n.left, optional = n.optional), ctx′)
     end
     tail′ = resolve(ctx)
@@ -506,6 +506,33 @@ function resolve(n::SelectNode, ctx)
     Resolved(RowType(fields), tail = q′)
 end
 
+function resolve(n::ShowNode, ctx)
+    tail′ = resolve(ctx)
+    t = row_type(tail′)
+    for name in n.names
+        ft = get(t.fields, name, EmptyType())
+        if ft isa EmptyType
+            throw(
+                ReferenceError(
+                    REFERENCE_ERROR_TYPE.UNDEFINED_NAME,
+                    name = name,
+                    path = get_path(ctx)))
+        end
+    end
+    fields = FieldTypeMap()
+    for (f, ft) in t.fields
+        if f in keys(n.label_map)
+            if ft isa ScalarType
+                ft = ScalarType(visible = n.visible)
+            else
+                ft = RowType(ft.fields, ft.group, visible = n.visible)
+            end
+        end
+        fields[f] = ft
+    end
+    Resolved(RowType(fields, t.group, visible = t.visible), tail = tail′)
+end
+
 function resolve_scalar(n::SortNode, ctx)
     tail′ = resolve_scalar(ctx)
     q′ = Sort(value = n.value, nulls = n.nulls, tail = tail′)
diff --git a/src/types.jl b/src/types.jl
index 856821ed..e04cfec6 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -13,17 +13,27 @@ PrettyPrinting.quoteof(::EmptyType) =
     Expr(:call, nameof(EmptyType))
 
 struct ScalarType <: AbstractSQLType
+    visible::Bool
+
+    ScalarType(; visible = true) =
+        new(visible)
 end
 
-PrettyPrinting.quoteof(::ScalarType) =
-    Expr(:call, nameof(ScalarType))
+function PrettyPrinting.quoteof(t::ScalarType)
+    ex = Expr(:call, nameof(ScalarType))
+    if !t.visible
+        push!(ex.args, Expr(:kw, :visible, t.visible))
+    end
+    ex
+end
 
 struct RowType <: AbstractSQLType
     fields::OrderedDict{Symbol, Union{ScalarType, RowType}}
     group::Union{EmptyType, RowType}
+    visible::Bool
 
-    RowType(fields, group = EmptyType()) =
-        new(fields, group)
+    RowType(fields, group = EmptyType(); visible = true) =
+        new(fields, group, visible)
 end
 
 const FieldTypeMap = OrderedDict{Symbol, Union{ScalarType, RowType}}
@@ -43,6 +53,9 @@ function PrettyPrinting.quoteof(t::RowType)
     if !(t.group isa EmptyType)
         push!(ex.args, Expr(:kw, :group, quoteof(t.group)))
     end
+    if !t.visible
+        push!(ex.args, Expr(:kw, :visible, t.visible))
+    end
     ex
 end
 
@@ -54,8 +67,8 @@ const EMPTY_ROW = RowType()
 Base.intersect(::AbstractSQLType, ::AbstractSQLType) =
     EmptyType()
 
-Base.intersect(::ScalarType, ::ScalarType) =
-    ScalarType()
+Base.intersect(t1::ScalarType, t2::ScalarType) =
+    ScalarType(visible = t1.visible || t2.visible)
 
 function Base.intersect(t1::RowType, t2::RowType)
     if t1 === t2
@@ -71,7 +84,7 @@ function Base.intersect(t1::RowType, t2::RowType)
         end
     end
     group = intersect(t1.group, t2.group)
-    RowType(fields, group)
+    RowType(fields, group, visible = t1.visible || t2.visible)
 end
 
 
@@ -98,5 +111,8 @@ function Base.issubset(t1::RowType, t2::RowType)
     if !issubset(t1.group, t2.group)
         return false
     end
+    if !t1.visible && t2.visible
+        return false
+    end
     return true
 end

From ff18dc057054eb2733b186577950ed1f757e571a Mon Sep 17 00:00:00 2001
From: Kyrylo Simonov <xi@resolvent.net>
Date: Wed, 5 Nov 2025 22:58:24 -0600
Subject: [PATCH 5/5] Replace show()/hide() with "private" parameter for
 define()/join()

---
 src/FunSQL.jl       |  2 --
 src/catalogs.jl     | 23 +++++++++------
 src/link.jl         |  3 +-
 src/nodes.jl        |  1 -
 src/nodes/define.jl | 20 ++++++++-----
 src/nodes/hide.jl   | 42 ---------------------------
 src/nodes/into.jl   | 19 +++++++-----
 src/nodes/join.jl   | 24 +++++++++-------
 src/nodes/show.jl   | 38 ------------------------
 src/resolve.jl      | 70 ++++++++++++++++++++++-----------------------
 src/types.jl        | 41 ++++++++++++--------------
 11 files changed, 107 insertions(+), 176 deletions(-)
 delete mode 100644 src/nodes/hide.jl
 delete mode 100644 src/nodes/show.jl

diff --git a/src/FunSQL.jl b/src/FunSQL.jl
index 56e4378a..618c6610 100644
--- a/src/FunSQL.jl
+++ b/src/FunSQL.jl
@@ -54,7 +54,6 @@ export
     funsql_from,
     funsql_fun,
     funsql_group,
-    funsql_hide,
     funsql_highlight,
     funsql_in,
     funsql_into,
@@ -84,7 +83,6 @@ export
     funsql_rank,
     funsql_row_number,
     funsql_select,
-    funsql_show,
     funsql_sort,
     funsql_sum,
     funsql_with
diff --git a/src/catalogs.jl b/src/catalogs.jl
index 0fbd446a..1fe7f2e6 100644
--- a/src/catalogs.jl
+++ b/src/catalogs.jl
@@ -31,22 +31,24 @@ _metadata_get(dict::SQLMetadata, key::Union{Symbol, AbstractString}, default; st
     end
 
 """
-    SQLColumn(; name, metadata = nothing)
-    SQLColumn(name; metadata = nothing)
+    SQLColumn(; name, private = false, metadata = nothing)
+    SQLColumn(name; private = false, metadata = nothing)
 
 `SQLColumn` represents a column with the given `name` and optional `metadata`.
+If `private` is `true`, the column is excluded from the default query output.
 """
 struct SQLColumn
     name::Symbol
+    private::Bool
     metadata::SQLMetadata
 
-    function SQLColumn(; name::Union{Symbol, AbstractString}, metadata = nothing)
-        new(Symbol(name), _metadata(metadata))
+    function SQLColumn(; name::Union{Symbol, AbstractString}, private = false, metadata = nothing)
+        new(Symbol(name), private, _metadata(metadata))
     end
 end
 
-SQLColumn(name; metadata = nothing) =
-    SQLColumn(name = name, metadata = metadata)
+SQLColumn(name; private = false, metadata = nothing) =
+    SQLColumn(; name, private, metadata)
 
 Base.show(io::IO, col::SQLColumn) =
     print(io, quoteof(col, limit = true))
@@ -56,6 +58,9 @@ Base.show(io::IO, ::MIME"text/plain", col::SQLColumn) =
 
 function PrettyPrinting.quoteof(col::SQLColumn; limit::Bool = false)
     ex = Expr(:call, nameof(SQLColumn), QuoteNode(col.name))
+    if col.private
+        push(ex.args, Expr(:kw, :private, col.private))
+    end
     if !isempty(col.metadata)
         push!(ex.args, Expr(:kw, :metadata, limit ? :… : quoteof(reverse!(collect(col.metadata)))))
     end
@@ -122,10 +127,10 @@ struct SQLTable <: AbstractDict{Symbol, SQLColumn}
 end
 
 SQLTable(name; qualifiers = Symbol[], columns, metadata = nothing) =
-    SQLTable(qualifiers = qualifiers, name = name, columns = columns, metadata = metadata)
+    SQLTable(; qualifiers, name, columns, metadata)
 
 SQLTable(name, columns...; qualifiers = Symbol[], metadata = nothing) =
-    SQLTable(qualifiers = qualifiers, name = name, columns = [columns...], metadata = metadata)
+    SQLTable(; qualifiers, name, columns = [columns...], metadata)
 
 _column_map(columns::OrderedDict{Symbol, SQLColumn}) =
     columns
@@ -280,7 +285,7 @@ struct SQLCatalog <: AbstractDict{Symbol, SQLTable}
 end
 
 SQLCatalog(tables...; dialect = :default, cache = default_cache_maxsize, metadata = nothing) =
-    SQLCatalog(tables = tables, dialect = dialect, cache = cache, metadata = metadata)
+    SQLCatalog(; tables, dialect, cache, metadata)
 
 _table_map(tables::Dict{Symbol, SQLTable}) =
     tables
diff --git a/src/link.jl b/src/link.jl
index c9eada38..8bb14e13 100644
--- a/src/link.jl
+++ b/src/link.jl
@@ -27,10 +27,9 @@ end
 
 function _select(t::RowType)
     refs = SQLQuery[]
-    t.visible || return refs
     for (f, ft) in t.fields
+        !(f in t.private_fields) || continue
         if ft isa ScalarType
-            ft.visible || continue
             push!(refs, Get(f))
         else
             nested_refs = _select(ft)
diff --git a/src/nodes.jl b/src/nodes.jl
index e16e70ef..b8e68a13 100644
--- a/src/nodes.jl
+++ b/src/nodes.jl
@@ -924,7 +924,6 @@ include("nodes/order.jl")
 include("nodes/over.jl")
 include("nodes/partition.jl")
 include("nodes/select.jl")
-include("nodes/show.jl")
 include("nodes/sort.jl")
 include("nodes/variable.jl")
 include("nodes/where.jl")
diff --git a/src/nodes/define.jl b/src/nodes/define.jl
index fab058de..3fd44dfc 100644
--- a/src/nodes/define.jl
+++ b/src/nodes/define.jl
@@ -4,13 +4,14 @@ struct DefineNode <: TabularNode
     args::Vector{SQLQuery}
     before::Union{Symbol, Bool}
     after::Union{Symbol, Bool}
+    private::Bool
     label_map::OrderedDict{Symbol, Int}
 
-    function DefineNode(; args = [], before = nothing, after = nothing, label_map = nothing)
+    function DefineNode(; args = [], before = nothing, after = nothing, private = false, label_map = nothing)
         if label_map !== nothing
-            n = new(args, something(before, false), something(after, false), label_map)
+            n = new(args, something(before, false), something(after, false), private, label_map)
         else
-            n = new(args, something(before, false), something(after, false), OrderedDict{Symbol, Int}())
+            n = new(args, something(before, false), something(after, false), private, OrderedDict{Symbol, Int}())
             populate_label_map!(n)
         end
         if (n.before isa Symbol || n.before) && (n.after isa Symbol || n.after)
@@ -20,12 +21,12 @@ struct DefineNode <: TabularNode
     end
 end
 
-DefineNode(args...; before = nothing, after = nothing) =
-    DefineNode(args = SQLQuery[args...], before = before, after = after)
+DefineNode(args...; before = nothing, after = nothing, private = false) =
+    DefineNode(args = SQLQuery[args...], before = before, after = after, private = private)
 
 """
-    Define(; args = [], before = nothing, after = nothing, tail = nothing)
-    Define(args...; before = nothing, after = nothing, tail = nothing)
+    Define(; args = [], before = nothing, after = nothing, private = false, tail = nothing)
+    Define(args...; before = nothing, after = nothing, private = false, tail = nothing)
 
 The `Define` node adds or replaces output columns.
 
@@ -35,6 +36,8 @@ both new and replaced columns at the end (after a specified column).
 Alternatively, set `before = true` (`before = <column>`) to add both new and
 replaced columns at the front (before the specified column).
 
+If `private` is set, the columns will be excluded from the query output.
+
 # Examples
 
 *Show patients who are at least 16 years old.*
@@ -90,5 +93,8 @@ function PrettyPrinting.quoteof(n::DefineNode, ctx::QuoteContext)
     if n.after !== false
         push!(ex.args, Expr(:kw, :after, n.after isa Symbol ? QuoteNode(n.after) : n.after))
     end
+    if n.private !== false
+        push!(ex.args, Expr(:kw, :private, n.private))
+    end
     ex
 end
diff --git a/src/nodes/hide.jl b/src/nodes/hide.jl
deleted file mode 100644
index 36ced02c..00000000
--- a/src/nodes/hide.jl
+++ /dev/null
@@ -1,42 +0,0 @@
-# Hide node
-
-mutable struct HideNode <: TabularNode
-    over::Union{SQLNode, Nothing}
-    names::Vector{Symbol}
-    label_map::FunSQL.OrderedDict{Symbol, Int}
-
-    function HideNode(; over = nothing, names = [], label_map = nothing)
-        if label_map !== nothing
-            new(over, names, label_map)
-        else
-            n = new(over, names, FunSQL.OrderedDict{Symbol, Int}())
-            for (i, name) in enumerate(n.names)
-                if name in keys(n.label_map)
-                    err = FunSQL.DuplicateLabelError(name, path = [n])
-                    throw(err)
-                end
-                n.label_map[name] = i
-            end
-            n
-        end
-    end
-end
-
-HideNode(names...; over = nothing) =
-    HideNode(over = over, names = Symbol[names...])
-
-Hide(args...; kws...) =
-    HideNode(args...; kws...) |> SQLNode
-
-const funsql_hide = Hide
-
-dissect(scr::Symbol, ::typeof(Hide), pats::Vector{Any}) =
-    dissect(scr, HideNode, pats)
-
-function FunSQL.PrettyPrinting.quoteof(n::HideNode, ctx::FunSQL.QuoteContext)
-    ex = Expr(:call, nameof(Hide), quoteof(n.names, ctx)...)
-    if n.over !== nothing
-        ex = Expr(:call, :|>, FunSQL.quoteof(n.over, ctx), ex)
-    end
-    ex
-end
diff --git a/src/nodes/into.jl b/src/nodes/into.jl
index f421ea1e..655652c0 100644
--- a/src/nodes/into.jl
+++ b/src/nodes/into.jl
@@ -2,17 +2,18 @@
 
 mutable struct IntoNode <: TabularNode
     name::Symbol
+    private::Bool
 
-    IntoNode(; name::Union{Symbol, AbstractString}) =
-        new(Symbol(name))
+    IntoNode(; name::Union{Symbol, AbstractString}, private::Bool = false) =
+        new(Symbol(name), private)
 end
 
-IntoNode(name) =
-    IntoNode(; name)
+IntoNode(name; private = false) =
+    IntoNode(; name, private)
 
 """
-    Into(; name, tail = nothing)
-    Into(name; tail = nothing)
+    Into(; name, private = false, tail = nothing)
+    Into(name; private = false, tail = nothing)
 
 `Into` wraps output columns in a nested record.
 """
@@ -21,7 +22,11 @@ const Into = SQLQueryCtor{IntoNode}(:Into)
 const funsql_into = Into
 
 function PrettyPrinting.quoteof(n::IntoNode, ctx::QuoteContext)
-    Expr(:call, :Into, quoteof(n.name))
+    ex = Expr(:call, :Into, quoteof(n.name))
+    if n.private
+        push!(ex.args, Expr(:kw, :private, n.private))
+    end
+    ex
 end
 
 label(n::IntoNode) =
diff --git a/src/nodes/join.jl b/src/nodes/join.jl
index 372d2272..027914f3 100644
--- a/src/nodes/join.jl
+++ b/src/nodes/join.jl
@@ -7,21 +7,22 @@ mutable struct JoinNode <: TabularNode
     right::Bool
     optional::Bool
     swap::Bool
+    private::Bool
 
-    JoinNode(; joinee, on, left = false, right = false, optional = false, swap = false) =
-        new(joinee, on, left, right, optional, swap)
+    JoinNode(; joinee, on, left = false, right = false, optional = false, swap = false, private = false) =
+        new(joinee, on, left, right, optional, swap, private)
 end
 
-JoinNode(joinee; on, left = false, right = false, optional = false, swap = false) =
-    JoinNode(; joinee, on, left, right, optional, swap)
+JoinNode(joinee; on, left = false, right = false, optional = false, swap = false, private = false) =
+    JoinNode(; joinee, on, left, right, optional, swap, private)
 
-JoinNode(joinee, on; left = false, right = false, optional = false, swap = false) =
-    JoinNode(; joinee, on, left, right, optional, swap)
+JoinNode(joinee, on; left = false, right = false, optional = false, swap = false, private = false) =
+    JoinNode(; joinee, on, left, right, optional, swap, private)
 
 """
-    Join(; joinee, on, left = false, right = false, optional = false, swap = false)
-    Join(joinee; on, left = false, right = false, optional = false, swap = false)
-    Join(joinee, on; left = false, right = false, optional = false, swap = false)
+    Join(; joinee, on, left = false, right = false, optional = false, swap = false, private = false)
+    Join(joinee; on, left = false, right = false, optional = false, swap = false, private = false)
+    Join(joinee, on; left = false, right = false, optional = false, swap = false, private = false)
 
 `Join` correlates two input datasets.
 
@@ -106,6 +107,9 @@ function PrettyPrinting.quoteof(n::JoinNode, ctx::QuoteContext)
         if n.swap
             push!(ex.args, Expr(:kw, :swap, n.swap))
         end
+        if n.private
+            push!(ex.args, Expr(:kw, :private, n.private))
+        end
     else
         push!(ex.args, :…)
     end
@@ -113,4 +117,4 @@ function PrettyPrinting.quoteof(n::JoinNode, ctx::QuoteContext)
 end
 
 label(n::JoinNode) =
-    n.swap ? label(n.joinee) : label(n.over)
+    n.swap ? label(n.joinee) : nothing
diff --git a/src/nodes/show.jl b/src/nodes/show.jl
deleted file mode 100644
index f0176ec7..00000000
--- a/src/nodes/show.jl
+++ /dev/null
@@ -1,38 +0,0 @@
-# Show/Hide nodes
-
-mutable struct ShowNode <: TabularNode
-    names::Vector{Symbol}
-    visible::Bool
-    label_map::FunSQL.OrderedDict{Symbol, Int}
-
-    function ShowNode(; names = [], visible = true, label_map = nothing)
-        if label_map !== nothing
-            new(names, visible, label_map)
-        else
-            n = new(names, visible, FunSQL.OrderedDict{Symbol, Int}())
-            for (i, name) in enumerate(n.names)
-                if name in keys(n.label_map)
-                    err = FunSQL.DuplicateLabelError(name, path = SQLQuery[n])
-                    throw(err)
-                end
-                n.label_map[name] = i
-            end
-            n
-        end
-    end
-end
-
-ShowNode(names...; visible = true) =
-    ShowNode(names = Symbol[names...], visible = visible)
-
-const Show = SQLQueryCtor{ShowNode}(:Show)
-
-Hide(args...; kws...) =
-    Show(args...; kws..., visible = false)
-
-const funsql_show = Show
-const funsql_hide = Hide
-
-function FunSQL.PrettyPrinting.quoteof(n::ShowNode, ctx::QuoteContext)
-    Expr(:call, n.visible ? :Show : :Hide, quoteof(n.names, ctx)...)
-end
diff --git a/src/resolve.jl b/src/resolve.jl
index 1e901673..2628e7f9 100644
--- a/src/resolve.jl
+++ b/src/resolve.jl
@@ -263,16 +263,28 @@ function resolve(n::DefineNode, ctx)
             end
         end
     end
+    private_fields = copy(t.private_fields)
+    for l in keys(n.label_map)
+        if n.private
+            push!(private_fields, l)
+        else
+            delete!(private_fields, l)
+        end
+    end
     q′ = Define(args = args′, label_map = n.label_map, tail = tail′)
-    Resolved(RowType(fields, t.group), tail = q′)
+    Resolved(RowType(fields, t.group, private_fields), tail = q′)
 end
 
 function RowType(table::SQLTable)
     fields = FieldTypeMap()
-    for f in keys(table.columns)
+    private_fields = Set{Symbol}()
+    for (f, c) in table.columns
         fields[f] = ScalarType()
+        if c.private
+            push!(private_fields, f)
+        end
     end
-    RowType(fields)
+    RowType(fields, EmptyType(), private_fields)
 end
 
 function resolve(n::FromNode, ctx)
@@ -390,8 +402,12 @@ function resolve(n::GroupNode, ctx)
         fields[n.name] = RowType(FieldTypeMap(), group)
         group = EmptyType()
     end
+    private_fields = Set{Symbol}()
+    if n.name !== nothing
+        push!(private_fields, n.name)
+    end
     q′ = Group(by = by′, sets = n.sets, label_map = n.label_map, tail = tail′)
-    Resolved(RowType(fields, group), tail = q′)
+    Resolved(RowType(fields, group, private_fields), tail = q′)
 end
 
 resolve(::HighlightNode, ctx) =
@@ -404,7 +420,8 @@ function resolve(n::IntoNode, ctx)
     tail′ = resolve(ctx)
     t = row_type(tail′)
     q′ = Into(name = n.name, tail = tail′)
-    Resolved(RowType(FieldTypeMap(n.name => t)), tail = q′)
+    t′ = RowType(FieldTypeMap(n.name => t), EmptyType(), n.private ? Set([n.name]) : Set{Symbol}())
+    Resolved(t′, tail = q′)
 end
 
 function resolve(n::IterateNode, ctx)
@@ -424,7 +441,7 @@ end
 function resolve(n::JoinNode, ctx)
     if n.swap
         ctx′ = ResolveContext(ctx, tail = n.joinee)
-        return resolve(JoinNode(joinee = ctx.tail, on = n.on, left = n.right, right = n.left, optional = n.optional), ctx′)
+        return resolve(JoinNode(joinee = ctx.tail, on = n.on, left = n.right, right = n.left, optional = n.optional, private = n.private), ctx′)
     end
     tail′ = resolve(ctx)
     lt = row_type(tail′)
@@ -437,7 +454,13 @@ function resolve(n::JoinNode, ctx)
     end
     fields[name] = rt
     group = lt.group
-    t = RowType(fields, group)
+    private_fields = copy(lt.private_fields)
+    if n.private
+        push!(private_fields, name)
+    else
+        delete!(private_fields, name)
+    end
+    t = RowType(fields, group, private_fields)
     on′ = resolve_scalar(n.on, ctx, t)
     q′ = RoutedJoin(joinee = joinee′, on = on′, name = name, left = n.left, right = n.right, optional = n.optional, tail = tail′)
     Resolved(t, tail = q′)
@@ -490,8 +513,12 @@ function resolve(n::PartitionNode, ctx)
         end
         fields[n.name] = RowType(FieldTypeMap(), t)
     end
+    private_fields = copy(t.private_fields)
+    if n.name !== nothing
+        push!(private_fields, n.name)
+    end
     q′ = Partition(by = by′, order_by = order_by′, frame = n.frame, name = n.name, tail = tail′)
-    Resolved(RowType(fields, group), tail = q′)
+    Resolved(RowType(fields, group, private_fields), tail = q′)
 end
 
 function resolve(n::SelectNode, ctx)
@@ -506,33 +533,6 @@ function resolve(n::SelectNode, ctx)
     Resolved(RowType(fields), tail = q′)
 end
 
-function resolve(n::ShowNode, ctx)
-    tail′ = resolve(ctx)
-    t = row_type(tail′)
-    for name in n.names
-        ft = get(t.fields, name, EmptyType())
-        if ft isa EmptyType
-            throw(
-                ReferenceError(
-                    REFERENCE_ERROR_TYPE.UNDEFINED_NAME,
-                    name = name,
-                    path = get_path(ctx)))
-        end
-    end
-    fields = FieldTypeMap()
-    for (f, ft) in t.fields
-        if f in keys(n.label_map)
-            if ft isa ScalarType
-                ft = ScalarType(visible = n.visible)
-            else
-                ft = RowType(ft.fields, ft.group, visible = n.visible)
-            end
-        end
-        fields[f] = ft
-    end
-    Resolved(RowType(fields, t.group, visible = t.visible), tail = tail′)
-end
-
 function resolve_scalar(n::SortNode, ctx)
     tail′ = resolve_scalar(ctx)
     q′ = Sort(value = n.value, nulls = n.nulls, tail = tail′)
diff --git a/src/types.jl b/src/types.jl
index e04cfec6..24d0c369 100644
--- a/src/types.jl
+++ b/src/types.jl
@@ -13,27 +13,21 @@ PrettyPrinting.quoteof(::EmptyType) =
     Expr(:call, nameof(EmptyType))
 
 struct ScalarType <: AbstractSQLType
-    visible::Bool
-
-    ScalarType(; visible = true) =
-        new(visible)
+    ScalarType() =
+        new()
 end
 
 function PrettyPrinting.quoteof(t::ScalarType)
-    ex = Expr(:call, nameof(ScalarType))
-    if !t.visible
-        push!(ex.args, Expr(:kw, :visible, t.visible))
-    end
-    ex
+    Expr(:call, nameof(ScalarType))
 end
 
 struct RowType <: AbstractSQLType
     fields::OrderedDict{Symbol, Union{ScalarType, RowType}}
     group::Union{EmptyType, RowType}
-    visible::Bool
+    private_fields::Set{Symbol}
 
-    RowType(fields, group = EmptyType(); visible = true) =
-        new(fields, group, visible)
+    RowType(fields, group = EmptyType(), private_fields = Set{Symbol}()) =
+        new(fields, group, private_fields)
 end
 
 const FieldTypeMap = OrderedDict{Symbol, Union{ScalarType, RowType}}
@@ -42,8 +36,8 @@ const GroupType = Union{EmptyType, RowType}
 RowType() =
     RowType(FieldTypeMap())
 
-RowType(fields::Pair{Symbol, <:AbstractSQLType}...; group = EmptyType()) =
-    RowType(FieldTypeMap(fields), group)
+RowType(fields::Pair{Symbol, <:AbstractSQLType}...; group = EmptyType(), private_fields = Set{Symbol}()) =
+    RowType(FieldTypeMap(fields), group, private_fields)
 
 function PrettyPrinting.quoteof(t::RowType)
     ex = Expr(:call, nameof(RowType))
@@ -53,8 +47,8 @@ function PrettyPrinting.quoteof(t::RowType)
     if !(t.group isa EmptyType)
         push!(ex.args, Expr(:kw, :group, quoteof(t.group)))
     end
-    if !t.visible
-        push!(ex.args, Expr(:kw, :visible, t.visible))
+    if !isempty(t.private_fields)
+        push!(ex.args, Expr(:kw, :private_fields, t.private_fields))
     end
     ex
 end
@@ -67,24 +61,28 @@ const EMPTY_ROW = RowType()
 Base.intersect(::AbstractSQLType, ::AbstractSQLType) =
     EmptyType()
 
-Base.intersect(t1::ScalarType, t2::ScalarType) =
-    ScalarType(visible = t1.visible || t2.visible)
+Base.intersect(::ScalarType, ::ScalarType) =
+    ScalarType()
 
 function Base.intersect(t1::RowType, t2::RowType)
     if t1 === t2
         return t1
     end
     fields = FieldTypeMap()
+    private_fields = Set{Symbol}()
     for f in keys(t1.fields)
         if f in keys(t2.fields)
             t = intersect(t1.fields[f], t2.fields[f])
             if !isa(t, EmptyType)
                 fields[f] = t
+                if f in t1.private_fields && f in t2.private_fields
+                    push!(private_fields, f)
+                end
             end
         end
     end
     group = intersect(t1.group, t2.group)
-    RowType(fields, group, visible = t1.visible || t2.visible)
+    RowType(fields, group, private_fields)
 end
 
 
@@ -104,15 +102,12 @@ function Base.issubset(t1::RowType, t2::RowType)
         return true
     end
     for f in keys(t1.fields)
-        if !(f in keys(t2.fields) && issubset(t1.fields[f], t2.fields[f]))
+        if !(f in keys(t2.fields) && issubset(t1.fields[f], t2.fields[f]) && (!(f in t1.private_fields) || f in t2.private_fields))
             return false
         end
     end
     if !issubset(t1.group, t2.group)
         return false
     end
-    if !t1.visible && t2.visible
-        return false
-    end
     return true
 end