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cherry pick pingcap#31742 to release-5.4
Signed-off-by: ti-srebot <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| // Copyright 2022 PingCAP, 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 agreed to 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 core | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "fmt" | ||
| "strings" | ||
|
|
||
| "github.com/pingcap/tidb/parser/ast" | ||
| driver "github.com/pingcap/tidb/types/parser_driver" | ||
| "github.com/pingcap/tidb/util/collate" | ||
| "github.com/pingcap/tidb/util/stringutil" | ||
| ) | ||
|
|
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| var _ ShowPredicateExtractor = &ShowColumnsTableExtractor{} | ||
|
|
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| // ShowPredicateExtractor is used to extract some predicates from `PatternLikeExpr` clause | ||
| // and push the predicates down to the data retrieving on reading memory table stage when use ShowStmt. | ||
| // | ||
| // e.g: | ||
| // SHOW COLUMNS FROM t LIKE '%abc%' | ||
| // We must request all components from the memory table, and filter the result by the PatternLikeExpr predicate. | ||
| // | ||
| // it is a way to fix https://github.com/pingcap/tidb/issues/29910. | ||
| type ShowPredicateExtractor interface { | ||
| // Extracts predicates which can be pushed down and returns whether the extractor can extract predicates. | ||
| Extract(show *ast.ShowStmt) bool | ||
| explainInfo() string | ||
| } | ||
|
|
||
| // ShowColumnsTableExtractor is used to extract some predicates of tables table. | ||
| type ShowColumnsTableExtractor struct { | ||
| Field string | ||
|
|
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| FieldPatterns string | ||
| } | ||
|
|
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| // Extract implements the MemTablePredicateExtractor Extract interface | ||
| func (e *ShowColumnsTableExtractor) Extract(show *ast.ShowStmt) bool { | ||
| if show.Pattern != nil && show.Pattern.Pattern != nil { | ||
| pattern := show.Pattern | ||
| switch pattern.Pattern.(type) { | ||
| case *driver.ValueExpr: | ||
| // It is used in `SHOW COLUMNS FROM t LIKE `abc``. | ||
| ptn := pattern.Pattern.(*driver.ValueExpr).GetString() | ||
| patValue, patTypes := stringutil.CompilePattern(ptn, pattern.Escape) | ||
| if !collate.NewCollationEnabled() && stringutil.IsExactMatch(patTypes) { | ||
| e.Field = strings.ToLower(string(patValue)) | ||
| return true | ||
| } | ||
| // (?i) mean to be case-insensitive. | ||
| e.FieldPatterns = "(?i)" + stringutil.CompileLike2Regexp(string(patValue)) | ||
| return true | ||
| case *ast.ColumnNameExpr: | ||
| // It is used in `SHOW COLUMNS FROM t LIKE abc`. | ||
| // MySQL do not support this syntax and return the error. | ||
| return false | ||
| } | ||
| } else if show.Column != nil && show.Column.Name.L != "" { | ||
| // it is used in `DESCRIBE t COLUMN`. | ||
| e.Field = show.Column.Name.L | ||
| return true | ||
| } | ||
| return false | ||
|
|
||
| } | ||
|
|
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| func (e *ShowColumnsTableExtractor) explainInfo() string { | ||
| r := new(bytes.Buffer) | ||
| if len(e.Field) > 0 { | ||
| r.WriteString(fmt.Sprintf("field:[%s], ", e.Field)) | ||
| } | ||
|
|
||
| if len(e.FieldPatterns) > 0 { | ||
| r.WriteString(fmt.Sprintf("field_pattern:[%s], ", e.FieldPatterns)) | ||
| } | ||
|
|
||
| // remove the last ", " in the message info | ||
| s := r.String() | ||
| if len(s) > 2 { | ||
| return s[:len(s)-2] | ||
| } | ||
| return s | ||
| } |
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