planner: fix the issue that TIDB_INLJ hint cannot take effect when le…

…ft joining two sub-queries (#46271) (#46291)

close #46160

executor/index_lookup_join_test.go

@@ -183,6 +183,16 @@ func TestInapplicableIndexJoinHint(t *testing.T) {
 	tk.MustQuery(`show warnings;`).Check(testkit.Rows(`Warning 1815 Optimizer Hint /*+ INL_MERGE_JOIN(t1) */ is inapplicable`))
 	tk.MustQuery(`select /*+ INL_MERGE_JOIN(t2) */ * from t1 right join t2 on t1.a=t2.a;`).Check(testkit.Rows())
 	tk.MustQuery(`show warnings;`).Check(testkit.Rows(`Warning 1815 Optimizer Hint /*+ INL_MERGE_JOIN(t2) */ is inapplicable`))
+
+	// Test for issues/46160
+	tk.MustExec(`drop table if exists t1, t2;`)
+	tk.MustExec("use test")
+	tk.MustExec(`create table t1 (a int, key(a))`)
+	tk.MustExec(`create table t2 (a int, key(a))`)
+
+	query := `select /*+ tidb_inlj(bb) */ aa.* from (select * from t1) as aa left join
+    (select t2.a, t2.a*2 as a2 from t2) as bb on aa.a=bb.a;`
+	tk.HasPlan(query, "IndexJoin")
 }
 
 func TestIndexJoinOverflow(t *testing.T) {

planner/core/logical_plan_builder.go

@@ -576,7 +576,8 @@ func extractTableAlias(p Plan, parentOffset int) *hintTableInfo {
 	if len(p.OutputNames()) > 0 && p.OutputNames()[0].TblName.L != "" {
 		firstName := p.OutputNames()[0]
 		for _, name := range p.OutputNames() {
-			if name.TblName.L != firstName.TblName.L || name.DBName.L != firstName.DBName.L {
+			if name.TblName.L != firstName.TblName.L ||
+				(name.DBName.L != "" && firstName.DBName.L != "" && name.DBName.L != firstName.DBName.L) { // DBName can be nil, see #46160
 				return nil
 			}
 		}