Added Unpivot. Fixed some Pivot (#2)

-- Technically, unpivot has some stricter
   expr requirements (eg instead of expr for ident in col_list
   it should be <column> for ident in col_list). I haven't been
   able to navigate to find this stricter definition yet, but
   maybe we want this fix ASAP.

Author: markwongsk

src/ast/query.rs

@@ -319,6 +319,14 @@ pub enum TableFactor {
     /// https://docs.snowflake.com/en/sql-reference/constructs/pivot.html
     Pivot {
         expr: Expr,
+        alias: Option<TableAlias>,
+        val: Ident,
+        pivot_vals: Vec<Expr>,
+    },
+    /// https://docs.snowflake.com/en/sql-reference/constructs/unpivot.html
+    Unpivot {
+        expr: Expr,
+        alias: Option<TableAlias>,
         val: Ident,
         pivot_vals: Vec<Expr>,
     },
@@ -389,6 +397,25 @@ impl fmt::Display for TableFactor {
             }
             TableFactor::Pivot {
                 expr,
+                alias,
+                val,
+                pivot_vals,
+            } => {
+                write!(f, "({} FOR {} IN (", expr, val)?;
+                let mut delim = "";
+                for pivot_val in pivot_vals {
+                    write!(f, "{}{}", delim, pivot_val)?;
+                    delim = ", ";
+                }
+                write!(f, "))")?;
+                if let Some(alias) = alias {
+                    write!(f, " AS {}", alias)?;
+                }
+                Ok(())
+            }
+            TableFactor::Unpivot {
+                expr,
+                alias,
                 val,
                 pivot_vals,
             } => {
@@ -398,7 +425,11 @@ impl fmt::Display for TableFactor {
                     write!(f, "{}{}", delim, pivot_val)?;
                     delim = ", ";
                 }
-                write!(f, "))")
+                write!(f, "))")?;
+                if let Some(alias) = alias {
+                    write!(f, " AS {}", alias)?;
+                }
+                Ok(())
             }
             TableFactor::NestedJoin(table_reference) => write!(f, "({})", table_reference),
         }

src/parser.rs

@@ -2631,6 +2631,7 @@ impl<'a> Parser<'a> {
                             alias.replace(outer_alias);
                         }
                         TableFactor::Pivot { .. } => unreachable!(),
+                        TableFactor::Unpivot { .. } => unreachable!(),
                         TableFactor::NestedJoin(_) => unreachable!(),
                     };
                 }
@@ -2681,8 +2682,10 @@ impl<'a> Parser<'a> {
         let pivot_vals = self.parse_comma_separated(Parser::parse_expr)?;
         self.expect_token(&Token::RParen)?;
         self.expect_token(&Token::RParen)?;
+        let alias = self.parse_optional_table_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?;
         Ok(TableFactor::Pivot {
             expr,
+            alias,
             val,
             pivot_vals,
         })