fix(compiler): handle subqueries in JOIN nullability inference

Fixed incorrect nullability inference when using subqueries with LEFT/RIGHT/FULL OUTER JOINs.

When using subqueries in JOINs like:
  SELECT * FROM a LEFT JOIN (SELECT * FROM b) si ON si.a_id = a.id

Columns from subquery 'si' were incorrectly treated as NOT NULL.

Root cause: The isTableRequired() function did not handle *ast.RangeSubselect (subquery ranges).

Solution:
- Added *ast.RangeSubselect case to isTableRequired()
- Match subqueries by their alias names
- Verified all JOIN types (LEFT/RIGHT/FULL OUTER) work correctly

Test coverage:
- Added internal/endtoend/testdata/join_left_subquery/postgresql/
- Covers LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN patterns

Fixes #4117

Author: kitagry

internal/compiler/output_columns.go

@@ -424,6 +424,13 @@ func isTableRequired(n ast.Node, col *Column, prior int) int {
 		if aliasMatch && tableMatch {
 			return prior
 		}
+	case *ast.RangeSubselect:
+		// For subqueries, match only by alias since there's no table name
+		if n.Alias != nil && col.TableAlias != "" {
+			if *n.Alias.Aliasname == col.TableAlias {
+				return prior
+			}
+		}
 	case *ast.JoinExpr:
 		helper := func(l, r int) int {
 			if res := isTableRequired(n.Larg, col, l); res != tableNotFound {

internal/endtoend/testdata/join_left_subquery/postgresql/go/db.go

@@ -0,0 +1,25 @@
+-- name: LeftJoinSubquery :many
+SELECT * FROM a AS table_a
+LEFT JOIN (SELECT * FROM b WHERE b.name IS NOT NULL) si ON si.a_id = table_a.id;
+
+-- name: LeftJoinSubqueryExplicitColumns :many
+SELECT
+    table_a.id,
+    table_a.name,
+    si.id,
+    si.a_id,
+    si.name
+FROM a AS table_a
+LEFT JOIN (SELECT id, a_id, name FROM b WHERE b.name IS NOT NULL) si ON si.a_id = table_a.id;
+
+-- name: LeftJoinSubqueryNoAlias :many
+SELECT * FROM a
+LEFT JOIN (SELECT * FROM b) subquery ON subquery.a_id = a.id;
+
+-- name: RightJoinSubquery :many
+SELECT * FROM a AS table_a
+RIGHT JOIN (SELECT * FROM b WHERE b.name IS NOT NULL) si ON si.a_id = table_a.id;
+
+-- name: FullOuterJoinSubquery :many
+SELECT * FROM a AS table_a
+FULL OUTER JOIN (SELECT * FROM b WHERE b.name IS NOT NULL) si ON si.a_id = table_a.id;

internal/endtoend/testdata/join_left_subquery/postgresql/go/models.go

@@ -0,0 +1,11 @@
+-- https://github.com/sqlc-dev/sqlc/issues/4117
+CREATE TABLE a (
+    id uuid PRIMARY KEY,
+    name TEXT
+);
+
+CREATE TABLE b (
+    id uuid PRIMARY KEY,
+    a_id uuid NOT NULL REFERENCES a (id),
+    name TEXT
+);

internal/endtoend/testdata/join_left_subquery/postgresql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "postgresql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}