From afdaa092697f4f188b53efd088915aed16e08a2d Mon Sep 17 00:00:00 2001
From: Yiding Cui <winoros@gmail.com>
Date: Thu, 18 Oct 2018 12:05:04 +0800
Subject: [PATCH] executor: fix a bug in point get (#7934)

---
 executor/point_get.go      | 46 +++++++++++++++++++++++++++-----------
 executor/point_get_test.go |  5 ++++-
 2 files changed, 37 insertions(+), 14 deletions(-)

diff --git a/executor/point_get.go b/executor/point_get.go
index cd150178843d..3d41181675bf 100644
--- a/executor/point_get.go
+++ b/executor/point_get.go
@@ -135,40 +135,60 @@ func (e *PointGetExecutor) get(key kv.Key) (val []byte, err error) {
 }
 
 func (e *PointGetExecutor) decodeRowValToChunk(rowVal []byte, chk *chunk.Chunk) error {
-	colIDs := make(map[int64]int, e.schema.Len())
-	for i, col := range e.schema.Columns {
-		colIDs[col.ID] = i
+	//  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)
+		}
 	}
-	colVals, err := tablecodec.CutRowNew(rowVal, colIDs)
+	decodedVals, err := tablecodec.CutRowNew(rowVal, colID2DecodedPos)
 	if err != nil {
 		return errors.Trace(err)
 	}
-	if colVals == nil {
-		colVals = make([][]byte, len(colIDs))
+	if decodedVals == nil {
+		decodedVals = make([][]byte, len(colID2DecodedPos))
 	}
 	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) {
-			chk.AppendInt64(offset, e.handle)
+	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])
+			}
 			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(offset, e.handle)
+			chk.AppendInt64(firstPos, e.handle)
 			continue
 		}
-		if len(colVals[offset]) == 0 {
+		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)
 			d, err1 := table.GetColOriginDefaultValue(e.ctx, colInfo)
 			if err1 != nil {
 				return errors.Trace(err1)
 			}
-			chk.AppendDatum(offset, &d)
+			chk.AppendDatum(firstPos, &d)
 			continue
 		}
-		_, err = decoder.DecodeOne(colVals[offset], offset, e.schema.Columns[offset].RetType)
+		_, err = decoder.DecodeOne(decodedVals[decodedPos], firstPos, e.schema.Columns[firstPos].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 5d0716618c85..65f8786ea7f7 100644
--- a/executor/point_get_test.go
+++ b/executor/point_get_test.go
@@ -38,7 +38,7 @@ func (s *testSuite) TestPointGet(c *C) {
 
 	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.MustExec(`insert into t values(1, NULL, NULL), (2, NULL, 2), (3, 3, NULL), (4, 4, 4), (5, 6, 7);`)
 	tk.MustQuery(`select * from t where a = 1;`).Check(testkit.Rows(
 		`1 <nil> <nil>`,
 	))
@@ -51,4 +51,7 @@ func (s *testSuite) TestPointGet(c *C) {
 	tk.MustQuery(`select * from t where a = 4;`).Check(testkit.Rows(
 		`4 4 4`,
 	))
+	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`,
+	))
 }