b3a52a05d5
[Update] Support update syntax
The current update syntax only supports updating the filtered data of a single table.
Syntax:
* UPDATE table_reference
* SET assignment_list
* [WHERE where_condition]
*
* value:
* {expr}
*
* assignment:
* col_name = value
*
* assignment_list:
* assignment [, assignment] ...
Example
Update unique_table
set v1=1
where k1=1
New Frontend Config: enable_concurrent_update
This configuration is used to control whether multi update stmt can be executed concurrently in one table.
Default value is false which means A table can only have one update task being executed at the same time.
If users want to update the same table concurrently,
they need to modify the configuration value to true and restart the master frontend.
Concurrent updates may cause write conflicts, the result is uncertain, please be careful.
The main realization principle:
1. Read the rows that meet the conditions according to the conditions set by where clause.
2. Modify the result of the row according to the set clause.
3. Write the modified row back to the table.
Some restrictions on the use of update syntax.
1. Only the unique table can be updated
2. Only the value column of the unique table can be updated
3. The where clause currently only supports single tables
Possible risks:
1. Since the current implementation method is a row update,
when the same table is updated concurrently, there may be concurrency conflicts which may cause the incorrect result.
2. Once the conditions of the where clause are unsatisfactory, it is likely to cause a full table scan and affect query performance.
Please pay attention to whether the column in the where clause can match the index when using it.
[Docs][Update] Add update document and sql-reference
Fixed #6229
76 lines
1.9 KiB
Markdown
76 lines
1.9 KiB
Markdown
---
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{
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"title": "UPDATE",
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"language": "zh-CN"
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}
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---
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<!--
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Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. 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 agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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# UPDATE
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## description
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### Syntax
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```
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UPDATE table_name
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SET assignment_list
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WHERE expression
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value:
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{expr | DEFAULT}
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assignment:
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col_name = value
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assignment_list:
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assignment [, assignment] ...
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```
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### Parameters
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+ table_name: 待更新数据的目标表。可以是 'db_name.table_name' 形式
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+ assignment_list: 待更新的目标列，形如 'col_name = value, col_name = value' 格式
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+ where expression: 期望更新的条件，一个返回 true 或者 false 的表达式即可
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### Note
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当前 UPDATE 语句仅支持在 Unique 模型上的行更新，存在并发更新导致的数据冲突可能。
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目前 Doris 并不处理这类问题，需要用户从业务侧规避这类问题。
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## example
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`test` 表是一个 unique 模型的表，包含: k1, k2, v1, v2 四个列。其中 k1, k2 是 key，v1, v2 是value，聚合方式是 Replace。
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1. 将 'test' 表中满足条件 k1 =1 , k2 =2 的 v1 列更新为 1
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```
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UPDATE test SET v1 = 1 WHERE k1=1 and k2=2;
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```
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2. 将 'test' 表中 k1=1 的列的 v1 列自增1
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```
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UPDATE test SET v1 = v1+1 WHERE k1=1;
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```
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## keyword
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UPDATE
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