You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
39 lines
1.4 KiB
39 lines
1.4 KiB
/*
|
|
Copyright 2017 Google Inc.
|
|
|
|
Licensed under the Apache License, Version 2.0 (the "License");
|
|
you may not use this file except in compliance with the License.
|
|
You may obtain a copy of the License at
|
|
|
|
http://www.apache.org/licenses/LICENSE-2.0
|
|
|
|
Unless required by applicable law or agreedto in writing, software
|
|
distributed under the License is distributed on an "AS IS" BASIS,
|
|
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
See the License for the specific language governing permissions and
|
|
limitations under the License.
|
|
*/
|
|
|
|
package sqlparser
|
|
|
|
// FormatImpossibleQuery creates an impossible query in a TrackedBuffer.
|
|
// An impossible query is a modified version of a query where all selects have where clauses that are
|
|
// impossible for mysql to resolve. This is used in the vtgate and vttablet:
|
|
//
|
|
// - In the vtgate it's used for joins: if the first query returns no result, then vtgate uses the impossible
|
|
// query just to fetch field info from vttablet
|
|
// - In the vttablet, it's just an optimization: the field info is fetched once form MySQL, cached and reused
|
|
// for subsequent queries
|
|
func FormatImpossibleQuery(buf *TrackedBuffer, node SQLNode) {
|
|
switch node := node.(type) {
|
|
case *Select:
|
|
buf.Myprintf("select %v from %v where 1 != 1", node.SelectExprs, node.From)
|
|
if node.GroupBy != nil {
|
|
node.GroupBy.Format(buf)
|
|
}
|
|
case *Union:
|
|
buf.Myprintf("%v %s %v", node.Left, node.Type, node.Right)
|
|
default:
|
|
node.Format(buf)
|
|
}
|
|
}
|
|
|