planner: push necessary predicates without virtual column down through UnionScan (#54985) (#55152)

close #54870

Author: qw4990

executor/union_scan_test.go

@@ -306,6 +306,20 @@ func TestUnionScanForMemBufferReader(t *testing.T) {
 	tk.MustExec("admin check table t1;")
 }
 
+func TestIssue54870(t *testing.T) {
+	store := testkit.CreateMockStore(t)
+	tk := testkit.NewTestKit(t, store)
+
+	tk.MustExec("use test")
+	tk.MustExec(`create table t (id int,
+deleted_at datetime(3) NOT NULL DEFAULT '1970-01-01 01:00:01.000',
+is_deleted tinyint(1) GENERATED ALWAYS AS ((deleted_at > _utf8mb4'1970-01-01 01:00:01.000')) VIRTUAL NOT NULL,
+key k(id, is_deleted))`)
+	tk.MustExec(`begin`)
+	tk.MustExec(`insert into t (id, deleted_at) values (1, now())`)
+	tk.MustHavePlan(`select 1 from t where id=1 and is_deleted=true`, "IndexRangeScan")
+}
+
 func TestIssue53951(t *testing.T) {
 	store := testkit.CreateMockStore(t)
 	tk := testkit.NewTestKit(t, store)

planner/core/rule_predicate_push_down.go

@@ -123,16 +123,22 @@ func (p *LogicalSelection) PredicatePushDown(predicates []expression.Expression,
 
 // PredicatePushDown implements LogicalPlan PredicatePushDown interface.
 func (p *LogicalUnionScan) PredicatePushDown(predicates []expression.Expression, opt *logicalOptimizeOp) ([]expression.Expression, LogicalPlan) {
-	if expression.ContainVirtualColumn(predicates) {
-		// predicates with virtual columns can't be pushed down to TiKV/TiFlash so they'll be put into a Projection
-		// below the UnionScan, but the current UnionScan doesn't support placing Projection below it, see #53951.
-		return predicates, p
+	var predicatesWithVCol, predicatesWithoutVCol []expression.Expression
+	// predicates with virtual columns can't be pushed down to TiKV/TiFlash so they'll be put into a Projection
+	// below the UnionScan, but the current UnionScan doesn't support placing Projection below it, see #53951.
+	for _, expr := range predicates {
+		if expression.ContainVirtualColumn([]expression.Expression{expr}) {
+			predicatesWithVCol = append(predicatesWithVCol, expr)
+		} else {
+			predicatesWithoutVCol = append(predicatesWithoutVCol, expr)
+		}
 	}
-
+	predicates = predicatesWithoutVCol
 	retainedPredicates, _ := p.children[0].PredicatePushDown(predicates, opt)
 	p.conditions = make([]expression.Expression, 0, len(predicates))
 	p.conditions = append(p.conditions, predicates...)
 	// The conditions in UnionScan is only used for added rows, so parent Selection should not be removed.
+	retainedPredicates = append(retainedPredicates, predicatesWithVCol...)
 	return retainedPredicates, p
 }