From a84eef567e93229f14866d76f0daabd4fbc2ae39 Mon Sep 17 00:00:00 2001
From: Haibin Xie <lambdax.tyler@gmail.com>
Date: Fri, 12 Jul 2019 14:11:14 +0800
Subject: [PATCH] executor: fix bug of point get when meet null values (#11219)

---
 executor/point_get.go      | 51 +++++++++++++-------------------------
 executor/point_get_test.go |  2 ++
 2 files changed, 19 insertions(+), 34 deletions(-)

diff --git a/executor/point_get.go b/executor/point_get.go
index cf351a777dbb8..e9dbed0617865 100644
--- a/executor/point_get.go
+++ b/executor/point_get.go
@@ -165,60 +165,43 @@ func (e *PointGetExecutor) get(key kv.Key) (val []byte, err error) {
 }
 
 func (e *PointGetExecutor) decodeRowValToChunk(rowVal []byte, chk *chunk.Chunk) error {
-	//  One column could be filled for multi-times in the schema. e.g. select b, b, c, c from t where a = 1.
-	// We need to set the positions in the schema for the same column.
-	colID2DecodedPos := make(map[int64]int, e.schema.Len())
-	decodedPos2SchemaPos := make([][]int, 0, e.schema.Len())
-	for schemaPos, col := range e.schema.Columns {
-		if decodedPos, ok := colID2DecodedPos[col.ID]; !ok {
-			colID2DecodedPos[col.ID] = len(colID2DecodedPos)
-			decodedPos2SchemaPos = append(decodedPos2SchemaPos, []int{schemaPos})
-		} else {
-			decodedPos2SchemaPos[decodedPos] = append(decodedPos2SchemaPos[decodedPos], schemaPos)
+	colID2CutPos := make(map[int64]int, e.schema.Len())
+	for _, col := range e.schema.Columns {
+		if _, ok := colID2CutPos[col.ID]; !ok {
+			colID2CutPos[col.ID] = len(colID2CutPos)
 		}
 	}
-	decodedVals, err := tablecodec.CutRowNew(rowVal, colID2DecodedPos)
+	cutVals, err := tablecodec.CutRowNew(rowVal, colID2CutPos)
 	if err != nil {
 		return errors.Trace(err)
 	}
-	if decodedVals == nil {
-		decodedVals = make([][]byte, len(colID2DecodedPos))
+	if cutVals == nil {
+		cutVals = make([][]byte, len(colID2CutPos))
 	}
 	decoder := codec.NewDecoder(chk, e.ctx.GetSessionVars().Location())
-	for id, decodedPos := range colID2DecodedPos {
-		schemaPoses := decodedPos2SchemaPos[decodedPos]
-		firstPos := schemaPoses[0]
-		if e.tblInfo.PKIsHandle && mysql.HasPriKeyFlag(e.schema.Columns[firstPos].RetType.Flag) {
-			chk.AppendInt64(firstPos, e.handle)
-			// Fill other positions.
-			for i := 1; i < len(schemaPoses); i++ {
-				chk.MakeRef(firstPos, schemaPoses[i])
-			}
+	for i, col := range e.schema.Columns {
+		if e.tblInfo.PKIsHandle && mysql.HasPriKeyFlag(col.RetType.Flag) {
+			chk.AppendInt64(i, e.handle)
 			continue
 		}
-		// ExtraHandleID is added when building plan, we can make sure that there's only one column's ID is this.
-		if id == model.ExtraHandleID {
-			chk.AppendInt64(firstPos, e.handle)
+		if col.ID == model.ExtraHandleID {
+			chk.AppendInt64(i, e.handle)
 			continue
 		}
-		if len(decodedVals[decodedPos]) == 0 {
-			// This branch only entered for updating and deleting. It won't have one column in multiple positions.
-			colInfo := getColInfoByID(e.tblInfo, id)
+		cutPos := colID2CutPos[col.ID]
+		if len(cutVals[cutPos]) == 0 {
+			colInfo := getColInfoByID(e.tblInfo, col.ID)
 			d, err1 := table.GetColOriginDefaultValue(e.ctx, colInfo)
 			if err1 != nil {
 				return errors.Trace(err1)
 			}
-			chk.AppendDatum(firstPos, &d)
+			chk.AppendDatum(i, &d)
 			continue
 		}
-		_, err = decoder.DecodeOne(decodedVals[decodedPos], firstPos, e.schema.Columns[firstPos].RetType)
+		_, err = decoder.DecodeOne(cutVals[cutPos], i, col.RetType)
 		if err != nil {
 			return errors.Trace(err)
 		}
-		// Fill other positions.
-		for i := 1; i < len(schemaPoses); i++ {
-			chk.MakeRef(firstPos, schemaPoses[i])
-		}
 	}
 	return nil
 }
diff --git a/executor/point_get_test.go b/executor/point_get_test.go
index f04c381354a49..cc7550e4f55bb 100644
--- a/executor/point_get_test.go
+++ b/executor/point_get_test.go
@@ -100,6 +100,8 @@ func (s *testPointGetSuite) TestPointGet(c *C) {
 	tk.MustQuery(`select a, a, b, a, b, c, b, c, c from t where a = 5;`).Check(testkit.Rows(
 		`5 5 6 5 6 7 6 7 7`,
 	))
+	tk.MustQuery(`select b, b from t where a = 1`).Check(testkit.Rows(
+		"<nil> <nil>"))
 }
 
 func (s *testPointGetSuite) TestPointGetCharPK(c *C) {