From 440eee57411eaa8f9b08a6fd78f124143f6e1d54 Mon Sep 17 00:00:00 2001
From: hanfei19910905 <hanfei19910905@gmail.com>
Date: Wed, 4 May 2016 11:07:44 +0800
Subject: [PATCH] push limit for incorrelate subquery.

---
 executor/subquery.go          |  1 +
 optimizer/plan/planbuilder.go | 11 ++++++-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/executor/subquery.go b/executor/subquery.go
index 121f04924c395..878f82f08a584 100644
--- a/executor/subquery.go
+++ b/executor/subquery.go
@@ -37,6 +37,7 @@ type subquery struct {
 func (sq *subquery) EvalRows(ctx context.Context, rowCount int) ([]types.Datum, error) {
 	b := newExecutorBuilder(ctx, sq.is)
 	plan.Refine(sq.plan)
+	plan.PushLimit(sq.plan, &ast.Limit{Count: 1})
 	e := b.build(sq.plan)
 	if b.err != nil {
 		return nil, errors.Trace(b.err)
diff --git a/optimizer/plan/planbuilder.go b/optimizer/plan/planbuilder.go
index 345665f5d4d15..bdc0e9646e1a5 100644
--- a/optimizer/plan/planbuilder.go
+++ b/optimizer/plan/planbuilder.go
@@ -266,7 +266,7 @@ func (b *planBuilder) buildSelect(sel *ast.SelectStmt) Plan {
 	}
 	if sel.Limit != nil {
 		if canPushLimit {
-			pushLimit(p, sel.Limit)
+			PushLimit(p, sel.Limit)
 		}
 		p = b.buildLimit(p, sel.Limit)
 		if b.err != nil {
@@ -594,7 +594,8 @@ func buildResultField(tableName, name string, tp byte, size int) *ast.ResultFiel
 	}
 }
 
-func pushLimit(p Plan, limit *ast.Limit) {
+// PushLimit tries to push limit count to the plan.
+func PushLimit(p Plan, limit *ast.Limit) {
 	switch x := p.(type) {
 	case *IndexScan:
 		limitCount := int64(limit.Offset + limit.Count)
@@ -605,7 +606,7 @@ func pushLimit(p Plan, limit *ast.Limit) {
 	default:
 		child := x.GetChildByIndex(0)
 		if child != nil {
-			pushLimit(child, limit)
+			PushLimit(child, limit)
 		}
 	}
 }
@@ -812,7 +813,7 @@ func (b *planBuilder) buildUpdate(update *ast.UpdateStmt) Plan {
 		}
 	}
 	if sel.Limit != nil {
-		pushLimit(p, sel.Limit)
+		PushLimit(p, sel.Limit)
 		p = b.buildLimit(p, sel.Limit)
 		if b.err != nil {
 			return nil
@@ -851,7 +852,7 @@ func (b *planBuilder) buildDelete(del *ast.DeleteStmt) Plan {
 		}
 	}
 	if sel.Limit != nil {
-		pushLimit(p, sel.Limit)
+		PushLimit(p, sel.Limit)
 		p = b.buildLimit(p, sel.Limit)
 		if b.err != nil {
 			return nil