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