The previous change actually destroyed the part of subquery

syntax that worked. A union without parentheses was actually
working. Now we're making the whole thing work. This introduces an
ambiguity, though, so we fix that with a %prec declaration.

Author: Martin Hansson

src/parser/bison_parser.y

@@ -319,6 +319,7 @@
 /* Unary Operators */
 %right    UMINUS
 %left     '[' ']'
+%left SUBQUERY_AS_EXPR
 %left     '(' ')'
 %left     '.'
 %left     JOIN
@@ -905,9 +906,9 @@ query_expression_parens : '(' query_expression_parens ')' { $$ = $2; }
 
 query_term : query_primary;
 
-subquery : '(' query_expression ')' { $$ = $2; };
+subquery : query_expression_parens % prec SUBQUERY_AS_EXPR
 
-set_operator : set_type opt_all {
+                                         set_operator : set_type opt_all {
   $$ = $1;
   $$->isAll = $2;
 };
@@ -1044,8 +1045,8 @@ expr : operand | between_expr | logic_expr | exists_expr | in_expr;
 
 operand : '(' expr ')' { $$ = $2; }
 | array_index | scalar_expr | unary_expr | binary_expr | case_expr | function_expr | extract_expr | cast_expr |
-    array_expr | '(' query_primary ')' {
-  $$ = Expr::makeSelect($2);
+    array_expr | subquery {
+  $$ = Expr::makeSelect($1);
 };
 
 scalar_expr : column_name | literal;

test/queries/queries-good.sql

@@ -18,6 +18,7 @@ SELECT * FROM t WHERE a = ? AND b = ?;
 SELECT City.name, Product.category, SUM(price) FROM fact INNER JOIN City ON fact.city_id = City.id INNER JOIN Product ON fact.product_id = Product.id GROUP BY City.name, Product.category;
 SELECT SUBSTR(a, 3, 5) FROM t;
 SELECT * FROM t WHERE a = DATE '1996-12-31';
+# Top-level union syntax
 SELECT 1 UNION SELECT 1;
 (SELECT 1 UNION SELECT 1);
 ((SELECT 1 UNION SELECT 1));
@@ -46,6 +47,16 @@ SELECT 1 UNION ((SELECT 1));
 ((SELECT 1)) UNION ((SELECT 1));
 (((SELECT 1)) UNION ((SELECT 1)));
 ((((SELECT 1)) UNION ((SELECT 1))));
+# Union in scalar subquery syntax
+SELECT (SELECT 1  UNION SELECT 1);
+SELECT ((SELECT 1) UNION SELECT 1);
+SELECT (((SELECT 1)) UNION SELECT 1);
+SELECT (SELECT 1 UNION (SELECT 1));
+SELECT (SELECT 1 UNION ((SELECT 1)));
+SELECT ((SELECT 1 UNION ((SELECT 1))));
+SELECT ((SELECT 1) UNION (SELECT 1));
+SELECT (((SELECT 1) UNION (SELECT 1)));
+SELECT ((((SELECT 1)) UNION ((SELECT 1))));
 # JOIN
 SELECT t1.a, t1.b, t2.c FROM "table" AS t1 JOIN (SELECT * FROM foo JOIN bar ON foo.id = bar.id) t2 ON t1.a = t2.b WHERE (t1.b OR NOT t1.a) AND t2.c = 12.5
 SELECT * FROM t1 JOIN t2 ON c1 = c2;