Merge pull request #578 from pingcap/qiuyesuifeng/dev-schema-change

Add/Drop column exist check.

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("column %s already exists", 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.
@@ -536,6 +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("column %s doesn’t exist", colName.L)
+	}
+
 	job := &model.Job{
 		SchemaID: schema.ID,
 		TableID:  t.Meta().ID,

ddl/ddl_db_test.go

@@ -190,7 +190,7 @@ LOOP:
 		delete(handles, h)
 	}
 
-	c.Assert(len(handles), Equals, 0)
+	c.Assert(handles, HasLen, 0)
 }
 
 func (s *testDBSuite) testDropIndex(c *C) {
@@ -258,7 +258,7 @@ LOOP:
 		handles[h] = struct{}{}
 	}
 
-	c.Assert(len(handles), Equals, 0)
+	c.Assert(handles, HasLen, 0)
 }
 
 func (s *testDBSuite) showColumns(c *C, tableName string) [][]interface{} {