Return a odpsResult instead of nil while running Exec

.gitignore

@@ -1,3 +1,6 @@
+nohup.out
+*~
+*.vim
 *~
 *.test
 /Gopkg.lock

connection.go

@@ -46,7 +46,11 @@ func (conn *odpsConn) Exec(query string, args []driver.Value) (driver.Result, er
 		return nil, err
 	}
 	_, err = conn.getInstanceResult(ins)
-	return nil, err
+	if err != nil {
+		return nil, err
+	}
+	// FIXME(weiguo): precise result
+	return &odpsResult{-1, -1}, nil
 }
 
 // Implements database/sql/driver.Queryer

result.go

@@ -0,0 +1,15 @@
+package gomaxcompute
+
+// odpsResult implements https://golang.org/pkg/database/sql/driver/#Result
+type odpsResult struct {
+	affectedRows int64
+	insertId     int64
+}
+
+func (res *odpsResult) LastInsertId() (int64, error) {
+	return res.insertId, nil
+}
+
+func (res *odpsResult) RowsAffected() (int64, error) {
+	return res.affectedRows, nil
+}