planner: Solve the problem that the parent query condition is pushed …

…incorrectly when the setvar function is evaluated in the subquery.(pingcap#11624)

expression/chunk_executor.go

@@ -53,6 +53,27 @@ func HasGetSetVarFunc(expr Expression) bool {
 	return false
 }
 
+// HasAssignSetVarFunc checks whether an expression contains SetVar function and assign a value
+func HasAssignSetVarFunc(expr Expression) bool {
+	scalaFunc, ok := expr.(*ScalarFunction)
+	if !ok {
+		return false
+	}
+	if scalaFunc.FuncName.L == ast.SetVar {
+		for _, arg := range scalaFunc.GetArgs() {
+			if _, ok := arg.(*ScalarFunction); ok {
+				return true
+			}
+		}
+	}
+	for _, arg := range scalaFunc.GetArgs() {
+		if HasAssignSetVarFunc(arg) {
+			return true
+		}
+	}
+	return false
+}
+
 // VectorizedExecute evaluates a list of expressions column by column and append their results to "output" Chunk.
 func VectorizedExecute(ctx sessionctx.Context, exprs []Expression, iterator *chunk.Iterator4Chunk, output *chunk.Chunk) error {
 	for colID, expr := range exprs {

planner/core/integration_test.go

@@ -189,3 +189,20 @@ func (s *testIntegrationSuite) TestAntiJoinConstProp(c *C) {
 		"1 <nil>",
 	))
 }
+
+func (s *testIntegrationSuite) TestPpdWithSetVar(c *C) {
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	tk := testkit.NewTestKit(c, store)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(c1 int, c2 varchar(255))")
+	tk.MustExec("insert into t values(1,'a'),(2,'d'),(3,'c')")
+
+	tk.MustQuery("select t01.c1,t01.c2,t01.c3 from (select t1.*,@c3:=@c3+1 as c3 from (select t.*,@c3:=0 from t order by t.c1)t1)t01 where t01.c3=1 and t01.c2='d'").Check(testkit.Rows())
+	tk.MustQuery("select t01.c1,t01.c2,t01.c3 from (select t1.*,@c3:=@c3+1 as c3 from (select t.*,@c3:=0 from t order by t.c1)t1)t01 where t01.c3=2 and t01.c2='d'").Check(testkit.Rows("2 d 2"))
+}

planner/core/rule_predicate_push_down.go

@@ -341,6 +341,12 @@ func isNullRejected(ctx sessionctx.Context, schema *expression.Schema, expr expr
 func (p *LogicalProjection) PredicatePushDown(predicates []expression.Expression) (ret []expression.Expression, retPlan LogicalPlan) {
 	canBePushed := make([]expression.Expression, 0, len(predicates))
 	canNotBePushed := make([]expression.Expression, 0, len(predicates))
+	for _, expr := range p.Exprs {
+		if expression.HasAssignSetVarFunc(expr) {
+			_, child := p.baseLogicalPlan.PredicatePushDown(nil)
+			return predicates, child
+		}
+	}
 	for _, cond := range predicates {
 		newFilter := expression.ColumnSubstitute(cond, p.Schema(), p.Exprs)
 		if !expression.HasGetSetVarFunc(newFilter) {