fix(binder): report error on update query with subquery on the set clause

src/frontend/planner_test/tests/testdata/input/update.yaml

@@ -98,3 +98,10 @@
     update t set a = a + 1;
   expected_outputs:
     - batch_distributed_plan
+- name: update table with subquery in the set clause
+  sql: |
+    create table t1 (v1 int primary key, v2 int);
+    create table t2 (v1 int primary key, v2 int);
+    update t1 set v1 = (select v1 from t2 where t1.v2 = t2.v2);
+  expected_outputs:
+    - binder_error

src/frontend/planner_test/tests/testdata/output/update.yaml

@@ -165,3 +165,9 @@
       └─BatchUpdate { table: t, exprs: [($0 + 1:Int32), $1, $2] }
         └─BatchExchange { order: [], dist: HashShard(t.a, t.b, t._row_id) }
           └─BatchScan { table: t, columns: [t.a, t.b, t._row_id], distribution: UpstreamHashShard(t._row_id) }
+- name: update table with subquery in the set clause
+  sql: |
+    create table t1 (v1 int primary key, v2 int);
+    create table t2 (v1 int primary key, v2 int);
+    update t1 set v1 = (select v1 from t2 where t1.v2 = t2.v2);
+  binder_error: 'Bind error: subquery on the right side of assignment is unsupported'

src/frontend/src/binder/update.rs

@@ -129,15 +129,17 @@ impl Binder {
         for Assignment { id, value } in assignments {
             // FIXME: Parsing of `id` is not strict. It will even treat `a.b` as `(a, b)`.
             let assignments = match (id.as_slice(), value) {
+                // _ = (subquery)
+                (_ids, AssignmentValue::Expr(Expr::Subquery(_))) => {
+                    return Err(ErrorCode::BindError(
+                        "subquery on the right side of assignment is unsupported".to_owned(),
+                    )
+                    .into())
+                }
                 // col = expr
                 ([id], value) => {
                     vec![(id.clone(), value)]
                 }
-
-                // (col1, col2) = (subquery)
-                (_ids, AssignmentValue::Expr(Expr::Subquery(_))) => {
-                    bail_not_implemented!("subquery on the right side of multi-assignment");
-                }
                 // (col1, col2) = (expr1, expr2)
                 // TODO: support `DEFAULT` in multiple assignments
                 (ids, AssignmentValue::Expr(Expr::Row(values))) if ids.len() == values.len() => id