From 31bbfcef82b2dcfbb230ada7421eb7f9e4a67c7c Mon Sep 17 00:00:00 2001
From: wjHuang <huangwenjun1997@gmail.com>
Date: Sat, 9 Jan 2021 13:19:14 +0800
Subject: [PATCH] executor: refine maxOneRow (#22194)

Signed-off-by: wjhuang2016 <huangwenjun1997@gmail.com>
---
 errors.toml               |  5 +++++
 executor/errors.go        | 17 +++++++++--------
 executor/executor.go      | 23 +++++++++++------------
 executor/executor_test.go |  2 +-
 4 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/errors.toml b/errors.toml
index ece8fae9df..1848a80016 100644
--- a/errors.toml
+++ b/errors.toml
@@ -491,6 +491,11 @@ error = '''
 Deadlock found when trying to get lock; try restarting transaction
 '''
 
+["executor:1242"]
+error = '''
+Subquery returns more than 1 row
+'''
+
 ["executor:1295"]
 error = '''
 This command is not supported in the prepared statement protocol yet
diff --git a/executor/errors.go b/executor/errors.go
index d648b56b81..afc6427690 100644
--- a/executor/errors.go
+++ b/executor/errors.go
@@ -20,14 +20,15 @@ import (
 
 // Error instances.
 var (
-	ErrGetStartTS      = dbterror.ClassExecutor.NewStd(mysql.ErrGetStartTS)
-	ErrUnknownPlan     = dbterror.ClassExecutor.NewStd(mysql.ErrUnknownPlan)
-	ErrPrepareMulti    = dbterror.ClassExecutor.NewStd(mysql.ErrPrepareMulti)
-	ErrPrepareDDL      = dbterror.ClassExecutor.NewStd(mysql.ErrPrepareDDL)
-	ErrResultIsEmpty   = dbterror.ClassExecutor.NewStd(mysql.ErrResultIsEmpty)
-	ErrBuildExecutor   = dbterror.ClassExecutor.NewStd(mysql.ErrBuildExecutor)
-	ErrBatchInsertFail = dbterror.ClassExecutor.NewStd(mysql.ErrBatchInsertFail)
-	ErrUnsupportedPs   = dbterror.ClassExecutor.NewStd(mysql.ErrUnsupportedPs)
+	ErrGetStartTS           = dbterror.ClassExecutor.NewStd(mysql.ErrGetStartTS)
+	ErrUnknownPlan          = dbterror.ClassExecutor.NewStd(mysql.ErrUnknownPlan)
+	ErrPrepareMulti         = dbterror.ClassExecutor.NewStd(mysql.ErrPrepareMulti)
+	ErrPrepareDDL           = dbterror.ClassExecutor.NewStd(mysql.ErrPrepareDDL)
+	ErrResultIsEmpty        = dbterror.ClassExecutor.NewStd(mysql.ErrResultIsEmpty)
+	ErrBuildExecutor        = dbterror.ClassExecutor.NewStd(mysql.ErrBuildExecutor)
+	ErrBatchInsertFail      = dbterror.ClassExecutor.NewStd(mysql.ErrBatchInsertFail)
+	ErrUnsupportedPs        = dbterror.ClassExecutor.NewStd(mysql.ErrUnsupportedPs)
+	ErrSubqueryMoreThan1Row = dbterror.ClassExecutor.NewStd(mysql.ErrSubqueryNo1Row)
 
 	ErrCantCreateUserWithGrant     = dbterror.ClassExecutor.NewStd(mysql.ErrCantCreateUserWithGrant)
 	ErrPasswordNoMatch             = dbterror.ClassExecutor.NewStd(mysql.ErrPasswordNoMatch)
diff --git a/executor/executor.go b/executor/executor.go
index c28cdaeab5..63f65f3d81 100644
--- a/executor/executor.go
+++ b/executor/executor.go
@@ -1152,17 +1152,16 @@ func init() {
 			return nil, err
 		}
 		chk := newFirstChunk(exec)
-		for {
-			err = Next(ctx, exec, chk)
-			if err != nil {
-				return nil, err
-			}
-			if chk.NumRows() == 0 {
-				return nil, nil
-			}
-			row := chk.GetRow(0).GetDatumRow(retTypes(exec))
-			return row, err
+
+		err = Next(ctx, exec, chk)
+		if err != nil {
+			return nil, err
 		}
+		if chk.NumRows() == 0 {
+			return nil, nil
+		}
+		row := chk.GetRow(0).GetDatumRow(retTypes(exec))
+		return row, err
 	}
 }
 
@@ -1393,7 +1392,7 @@ func (e *MaxOneRowExec) Next(ctx context.Context, req *chunk.Chunk) error {
 		}
 		return nil
 	} else if num != 1 {
-		return errors.New("subquery returns more than 1 row")
+		return ErrSubqueryMoreThan1Row
 	}
 
 	childChunk := newFirstChunk(e.children[0])
@@ -1402,7 +1401,7 @@ func (e *MaxOneRowExec) Next(ctx context.Context, req *chunk.Chunk) error {
 		return err
 	}
 	if childChunk.NumRows() != 0 {
-		return errors.New("subquery returns more than 1 row")
+		return ErrSubqueryMoreThan1Row
 	}
 
 	return nil
diff --git a/executor/executor_test.go b/executor/executor_test.go
index 1e0c3676ef..8216cf9833 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -4150,7 +4150,7 @@ func (s *testSuite3) TestMaxOneRow(c *C) {
 	c.Assert(err, IsNil)
 
 	err = rs.Next(context.TODO(), rs.NewChunk())
-	c.Assert(err.Error(), Equals, "subquery returns more than 1 row")
+	c.Assert(err.Error(), Equals, "[executor:1242]Subquery returns more than 1 row")
 
 	err = rs.Close()
 	c.Assert(err, IsNil)