executor: fix table id to partition id mapping in select lock executor (#26380)

executor/executor.go

@@ -929,8 +929,9 @@ func (e *SelectLockExec) Next(ctx context.Context, req *chunk.Chunk) error {
 				if len(e.partitionedTable) > 0 {
 					// Replace the table ID with partition ID.
 					// The partition ID is returned as an extra column from the table reader.
-					offset := e.tblID2PIDColumnIndex[id]
-					physicalID = row.GetInt64(offset)
+					if offset, ok := e.tblID2PIDColumnIndex[id]; ok {
+						physicalID = row.GetInt64(offset)
+					}
 				}
 
 				for _, col := range cols {

executor/partition_table_test.go

@@ -3055,3 +3055,35 @@ func (s *partitionTableSuite) TestIssue25528(c *C) {
 	tk.MustExec("INSERT INTO issue25528 (`c1`, `c2`, `c3`, `c4`) VALUES (1, 1, 1, 1) , (3, 3, 3, 3) , (2, 2, 2, 2) , (4, 4, 4, 4);")
 	tk.MustQuery("select * from issue25528 where c1 in (3, 4) order by c2 for update;").Check(testkit.Rows("3 3 3 3", "4 4 4 4"))
 }
+
+func (s *partitionTableSuite) TestIssue26251(c *C) {
+	tk1 := testkit.NewTestKit(c, s.store)
+	tk1.MustExec("use test")
+	tk1.MustExec("create table tp (id int primary key) partition by range (id) (partition p0 values less than (100));")
+	tk1.MustExec("create table tn (id int primary key);")
+	tk1.MustExec("insert into tp values(1),(2);")
+	tk1.MustExec("insert into tn values(1),(2);")
+
+	tk2 := testkit.NewTestKit(c, s.store)
+	tk2.MustExec("use test")
+
+	tk1.MustExec("begin pessimistic")
+	tk1.MustQuery("select * from tp,tn where tp.id=tn.id and tn.id<=1 for update;").Check(testkit.Rows("1 1"))
+
+	ch := make(chan struct{}, 1)
+	tk2.MustExec("begin pessimistic")
+	go func() {
+		// This query should block.
+		tk2.MustQuery("select * from tn where id=1 for update;").Check(testkit.Rows("1"))
+		ch <- struct{}{}
+	}()
+
+	select {
+	case <-time.After(100 * time.Millisecond):
+		// Expected, query blocked, not finish within 100ms.
+		tk1.MustExec("rollback")
+	case <-ch:
+		// Unexpected, test fail.
+		c.Fail()
+	}
+}