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[release-22.0] Fix cross shard/keyspace joins with derived tables containing a UNION. (#19046) #19136

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Merged
arthurschreiber merged 2 commits into from
Jan 15, 2026
Merged

[release-22.0] Fix cross shard/keyspace joins with derived tables containing a UNION. (#19046) #19136

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d680ff0
Cherry-pick 737e635fbde13a302c4a0e3dc50319c634ddefd0 with conflicts
vitess-bot[bot] Jan 13, 2026
6301e8b
Fix merge conflict.
arthurschreiber Jan 14, 2026
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9 changes: 9 additions & 0 deletions go/vt/vtgate/planbuilder/operators/union.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ import (
"vitess.io/vitess/go/slice"
"vitess.io/vitess/go/vt/sqlparser"
"vitess.io/vitess/go/vt/vterrors"
"vitess.io/vitess/go/vt/vtgate/planbuilder/operators/predicates"
"vitess.io/vitess/go/vt/vtgate/planbuilder/plancontext"
)

Expand Down Expand Up @@ -103,6 +104,11 @@ func (u *Union) AddPredicate(ctx *plancontext.PlanningContext, expr sqlparser.Ex
offsets[ae.ColumnName()] = i
}

if jp, ok := expr.(*predicates.JoinPredicate); ok {
expr = jp.Current()
ctx.PredTracker.Skip(jp.ID)
}

needsFilter, exprPerSource := u.predicatePerSource(expr, offsets)
if needsFilter {
return newFilter(u, expr)
Expand All @@ -118,6 +124,7 @@ func (u *Union) AddPredicate(ctx *plancontext.PlanningContext, expr sqlparser.Ex
func (u *Union) predicatePerSource(expr sqlparser.Expr, offsets map[string]int) (bool, []sqlparser.Expr) {
needsFilter := false
exprPerSource := make([]sqlparser.Expr, len(u.Sources))

for i := range u.Sources {
predicate := sqlparser.CopyOnRewrite(expr, nil, func(cursor *sqlparser.CopyOnWriteCursor) {
col, ok := cursor.Node().(*sqlparser.ColName)
Expand All @@ -137,11 +144,13 @@ func (u *Union) predicatePerSource(expr sqlparser.Expr, offsets map[string]int)
if !ok {
panic(vterrors.VT09015())
}

cursor.Replace(ae.Expr)
}, nil).(sqlparser.Expr)

exprPerSource[i] = predicate
}

return needsFilter, exprPerSource
}

Expand Down
74 changes: 74 additions & 0 deletions go/vt/vtgate/planbuilder/testdata/union_cases.json
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Original file line number Diff line number Diff line change
Expand Up @@ -2086,5 +2086,79 @@
"user.user"
]
}
},
{
"comment": "join with derived table containing UNION with aliased columns across different keyspaces",
"query": "select u.id from user as u join (select id as pid from user where id = 1 union select id as pid from unsharded where id = 1) as i on u.id = i.pid",
"plan": {
"Type": "Join",
"QueryType": "SELECT",
"Original": "select u.id from user as u join (select id as pid from user where id = 1 union select id as pid from unsharded where id = 1) as i on u.id = i.pid",
"Instructions": {
"OperatorType": "Join",
"Variant": "Join",
"JoinColumnIndexes": "L:0",
"JoinVars": {
"u_id": 0
},
"TableName": "`user`_`user`_unsharded",
"Inputs": [
{
"OperatorType": "Route",
"Variant": "Scatter",
"Keyspace": {
"Name": "user",
"Sharded": true
},
"FieldQuery": "select u.id from `user` as u where 1 != 1",
"Query": "select u.id from `user` as u",
"Table": "`user`"
},
{
"OperatorType": "Distinct",
"Collations": [
"(0:1)"
],
"Inputs": [
{
"OperatorType": "Concatenate",
"Inputs": [
{
"OperatorType": "Route",
"Variant": "EqualUnique",
"Keyspace": {
"Name": "user",
"Sharded": true
},
"FieldQuery": "select dt.c0 as pid, weight_string(dt.c0) from (select id as pid from `user` where 1 != 1) as dt(c0) where 1 != 1",
"Query": "select dt.c0 as pid, weight_string(dt.c0) from (select distinct id as pid from `user` where id = 1 and id = :u_id) as dt(c0)",
"Table": "`user`",
"Values": [
":u_id"
],
"Vindex": "user_index"
},
{
"OperatorType": "Route",
"Variant": "Unsharded",
"Keyspace": {
"Name": "main",
"Sharded": false
},
"FieldQuery": "select dt.c0 as pid, weight_string(dt.c0) from (select id as pid from unsharded where 1 != 1) as dt(c0) where 1 != 1",
"Query": "select dt.c0 as pid, weight_string(dt.c0) from (select distinct id as pid from unsharded where id = 1 and id = :u_id) as dt(c0)",
"Table": "unsharded"
}
]
}
]
}
]
},
"TablesUsed": [
"main.unsharded",
"user.user"
]
}
}
]
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