executor: fix point get null values (#7790)

Author: zz-jason

executor/point_get.go

@@ -143,6 +143,9 @@ func (e *PointGetExecutor) decodeRowValToChunk(rowVal []byte, chk *chunk.Chunk)
 	if err != nil {
 		return errors.Trace(err)
 	}
+	if colVals == nil {
+		colVals = make([][]byte, len(colIDs))
+	}
 	decoder := codec.NewDecoder(chk, e.ctx.GetSessionVars().Location())
 	for id, offset := range colIDs {
 		if e.tblInfo.PKIsHandle && mysql.HasPriKeyFlag(e.schema.Columns[offset].RetType.Flag) {
@@ -153,8 +156,7 @@ func (e *PointGetExecutor) decodeRowValToChunk(rowVal []byte, chk *chunk.Chunk)
 			chk.AppendInt64(offset, e.handle)
 			continue
 		}
-		colVal := colVals[offset]
-		if len(colVal) == 0 {
+		if len(colVals[offset]) == 0 {
 			colInfo := getColInfoByID(e.tblInfo, id)
 			d, err1 := table.GetColOriginDefaultValue(e.ctx, colInfo)
 			if err1 != nil {

executor/point_get_test.go

@@ -35,4 +35,20 @@ func (s *testSuite) TestPointGet(c *C) {
 	tk.MustExec("CREATE UNIQUE INDEX idx_tab3_0 ON tab3 (col4);")
 	tk.MustExec("INSERT INTO tab3 VALUES(0,854,111.96,'mguub',711,966.36,'snwlo');")
 	tk.MustQuery("SELECT ALL * FROM tab3 WHERE col4 = 85;").Check(testkit.Rows())
+
+	tk.MustExec(`drop table if exists t;`)
+	tk.MustExec(`create table t(a bigint primary key, b bigint, c bigint);`)
+	tk.MustExec(`insert into t values(1, NULL, NULL), (2, NULL, 2), (3, 3, NULL), (4, 4, 4);`)
+	tk.MustQuery(`select * from t where a = 1;`).Check(testkit.Rows(
+		`1 <nil> <nil>`,
+	))
+	tk.MustQuery(`select * from t where a = 2;`).Check(testkit.Rows(
+		`2 <nil> 2`,
+	))
+	tk.MustQuery(`select * from t where a = 3;`).Check(testkit.Rows(
+		`3 3 <nil>`,
+	))
+	tk.MustQuery(`select * from t where a = 4;`).Check(testkit.Rows(
+		`4 4 4`,
+	))
 }