From fccaf9b1f52e2e5262463a8374d570a913bc98b3 Mon Sep 17 00:00:00 2001
From: qiuyesuifeng <cuiqiu.bupt@gmail.com>
Date: Thu, 12 Nov 2015 11:49:44 +0800
Subject: [PATCH 1/3] ddl: add column exist check.

---
 ddl/ddl.go         | 8 +++++++-
 ddl/ddl_db_test.go | 4 ++--
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/ddl/ddl.go b/ddl/ddl.go
index 2d18b9d338..d0753f1e84 100644
--- a/ddl/ddl.go
+++ b/ddl/ddl.go
@@ -502,7 +502,13 @@ func (d *ddl) AddColumn(ctx context.Context, ti table.Ident, spec *AlterSpecific
 		return errors.Trace(ErrNotExists)
 	}
 
-	var col *column.Col
+	// Check whether added column has existed.
+	colName := spec.Column.Name
+	col := column.FindCol(t.Cols(), colName)
+	if col != nil {
+		return errors.Errorf("Try to add a column with the same name of an already exists column - %s", colName)
+	}
+
 	// ingore table constraints now, maybe return error later
 	// we use length(t.Cols()) as the default offset first, later we will change the
 	// column's offset later.
diff --git a/ddl/ddl_db_test.go b/ddl/ddl_db_test.go
index 02b6237345..8ea55ec53a 100644
--- a/ddl/ddl_db_test.go
+++ b/ddl/ddl_db_test.go
@@ -187,7 +187,7 @@ LOOP:
 		delete(handles, h)
 	}
 
-	c.Assert(len(handles), Equals, 0)
+	c.Assert(handles, HasLen, 0)
 }
 
 func (s *testDBSuite) testDropIndex(c *C) {
@@ -255,7 +255,7 @@ LOOP:
 		handles[h] = struct{}{}
 	}
 
-	c.Assert(len(handles), Equals, 0)
+	c.Assert(handles, HasLen, 0)
 }
 
 func (s *testDBSuite) showColumns(c *C, tableName string) [][]interface{} {

From cbf4732a540ffe34379279ab236475a3afc47288 Mon Sep 17 00:00:00 2001
From: qiuyesuifeng <cuiqiu.bupt@gmail.com>
Date: Thu, 12 Nov 2015 12:28:34 +0800
Subject: [PATCH 2/3] ddl: drop column exist check.

---
 ddl/ddl.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/ddl/ddl.go b/ddl/ddl.go
index d0753f1e84..93f5bf97a8 100644
--- a/ddl/ddl.go
+++ b/ddl/ddl.go
@@ -542,6 +542,12 @@ func (d *ddl) DropColumn(ctx context.Context, ti table.Ident, colName model.CISt
 		return errors.Trace(ErrNotExists)
 	}
 
+	// Check whether dropped column has existed.
+	col := column.FindCol(t.Cols(), colName.L)
+	if col == nil {
+		return errors.Errorf("Try to drop a none exist column - %s", colName.L)
+	}
+
 	job := &model.Job{
 		SchemaID: schema.ID,
 		TableID:  t.Meta().ID,

From 840249541f3710d244221f3e4064583f5e868ef5 Mon Sep 17 00:00:00 2001
From: qiuyesuifeng <cuiqiu.bupt@gmail.com>
Date: Thu, 12 Nov 2015 12:42:31 +0800
Subject: [PATCH 3/3] ddl: address comment.

---
 ddl/ddl.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ddl/ddl.go b/ddl/ddl.go
index 93f5bf97a8..8d16b6658e 100644
--- a/ddl/ddl.go
+++ b/ddl/ddl.go
@@ -506,7 +506,7 @@ func (d *ddl) AddColumn(ctx context.Context, ti table.Ident, spec *AlterSpecific
 	colName := spec.Column.Name
 	col := column.FindCol(t.Cols(), colName)
 	if col != nil {
-		return errors.Errorf("Try to add a column with the same name of an already exists column - %s", colName)
+		return errors.Errorf("column %s already exists", colName)
 	}
 
 	// ingore table constraints now, maybe return error later
@@ -545,7 +545,7 @@ func (d *ddl) DropColumn(ctx context.Context, ti table.Ident, colName model.CISt
 	// Check whether dropped column has existed.
 	col := column.FindCol(t.Cols(), colName.L)
 	if col == nil {
-		return errors.Errorf("Try to drop a none exist column - %s", colName.L)
+		return errors.Errorf("column %s doesn’t exist", colName.L)
 	}
 
 	job := &model.Job{