plan/executor: handle optimizer hint properly for cartesian join

executor/merge_join.go

@@ -84,7 +84,7 @@ type mergeJoinInnerTable struct {
 }
 
 func (t *mergeJoinInnerTable) init(ctx context.Context, chk4Reader *chunk.Chunk) (err error) {
-	if t.reader == nil || t.joinKeys == nil || len(t.joinKeys) == 0 || ctx == nil {
+	if t.reader == nil || ctx == nil {
 		return errors.Errorf("Invalid arguments: Empty arguments detected.")
 	}
 	t.ctx = ctx

plan/gen_physical_plans.go

@@ -359,12 +359,16 @@ func (p *LogicalJoin) buildFakeEqCondsForIndexJoin(keys, idxCols []*expression.C
 // tryToGetIndexJoin will get index join by hints. If we can generate a valid index join by hint, the second return value
 // will be true, which means we force to choose this index join. Otherwise we will select a join algorithm with min-cost.
 func (p *LogicalJoin) tryToGetIndexJoin(prop *requiredProp) ([]PhysicalPlan, bool) {
-	if len(p.EqualConditions) == 0 {
-		return nil, false
-	}
 	plans := make([]PhysicalPlan, 0, 2)
 	leftOuter := (p.preferJoinType & preferLeftAsIndexOuter) > 0
 	rightOuter := (p.preferJoinType & preferRightAsIndexOuter) > 0
+	if len(p.EqualConditions) == 0 {
+		if leftOuter || rightOuter {
+			warning := ErrInternal.GenByArgs("TIDB_INLJ hint is inapplicable without column equal ON condition")
+			p.ctx.GetSessionVars().StmtCtx.AppendWarning(warning)
+		}
+		return nil, false
+	}
 	switch p.JoinType {
 	case SemiJoin, AntiSemiJoin, LeftOuterSemiJoin, AntiLeftOuterSemiJoin, LeftOuterJoin:
 		join := p.getIndexJoinByOuterIdx(prop, 0)

plan/physical_plan_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/pingcap/tidb/plan"
 	"github.com/pingcap/tidb/session"
 	"github.com/pingcap/tidb/sessionctx"
+	"github.com/pingcap/tidb/terror"
 	"github.com/pingcap/tidb/util/testleak"
 	"golang.org/x/net/context"
 )
@@ -1248,3 +1249,27 @@ func (s *testPlanSuite) TestRequestTypeSupportedOff(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(plan.ToString(p), Equals, expect, Commentf("for %s", sql))
 }
+
+func (s *testPlanSuite) TestIndexLookupCartesianJoin(c *C) {
+	defer testleak.AfterTest(c)()
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+	se, err := session.CreateSession4Test(store)
+	c.Assert(err, IsNil)
+	_, err = se.Execute(context.Background(), "use test")
+	c.Assert(err, IsNil)
+	sql := "select /*+ TIDB_INLJ(t1, t2) */ * from t t1 join t t2"
+	stmt, err := s.ParseOneStmt(sql, "", "")
+	c.Assert(err, IsNil)
+	p, err := plan.Optimize(se, stmt, s.is)
+	c.Assert(err, IsNil)
+	c.Assert(plan.ToString(p), Equals, "LeftHashJoin{TableReader(Table(t))->TableReader(Table(t))}")
+	warnings := se.GetSessionVars().StmtCtx.GetWarnings()
+	lastWarn := warnings[len(warnings)-1]
+	err = plan.ErrInternal.GenByArgs("TIDB_INLJ hint is inapplicable without column equal ON condition")
+	c.Assert(terror.ErrorEqual(err, lastWarn.Err), IsTrue)
+}