planner: cannot simply outer join if a predicate just refers to the o…

…uter table (#16444)

planner/core/logical_plan_test.go

@@ -1579,3 +1579,23 @@ func (s *testPlanSuite) TestConflictedJoinTypeHints(c *C) {
 	c.Assert(join.hintInfo, IsNil)
 	c.Assert(join.preferJoinType, Equals, uint(0))
 }
+
+func (s *testPlanSuite) TestSimplyOuterJoinWithOnlyOuterExpr(c *C) {
+	defer testleak.AfterTest(c)()
+	sql := "select * from t t1 right join t t0 ON TRUE where CONCAT_WS(t0.e=t0.e, 0, NULL) IS NULL"
+	ctx := context.TODO()
+	stmt, err := s.ParseOneStmt(sql, "", "")
+	c.Assert(err, IsNil)
+	Preprocess(s.ctx, stmt, s.is)
+	builder := NewPlanBuilder(MockContext(), s.is, &hint.BlockHintProcessor{})
+	p, err := builder.Build(ctx, stmt)
+	c.Assert(err, IsNil)
+	p, err = logicalOptimize(ctx, builder.optFlag, p.(LogicalPlan))
+	c.Assert(err, IsNil)
+	proj, ok := p.(*LogicalProjection)
+	c.Assert(ok, IsTrue)
+	join, ok := proj.Children()[0].(*LogicalJoin)
+	c.Assert(ok, IsTrue)
+	// previous wrong JoinType is InnerJoin
+	c.Assert(join.JoinType, Equals, RightOuterJoin)
+}

planner/core/rule_predicate_push_down.go

@@ -316,6 +316,10 @@ func simplifyOuterJoin(p *LogicalJoin, predicates []expression.Expression) {
 	// then simplify embedding outer join.
 	canBeSimplified := false
 	for _, expr := range predicates {
+		// avoid the case where the expr only refers to the schema of outerTable
+		if expression.ExprFromSchema(expr, outerTable.Schema()) {
+			continue
+		}
 		isOk := isNullRejected(p.ctx, innerTable.Schema(), expr)
 		if isOk {
 			canBeSimplified = true