73 lines
1.9 KiB
Markdown
73 lines
1.9 KiB
Markdown
---
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{
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"title": "case",
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"language": "en"
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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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## case
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### description
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#### Syntax
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```
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CASE expression
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WHEN condition1 THEN result1
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[WHEN condition2 THEN result2]
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...
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[WHEN conditionN THEN resultN]
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[ELSE result]
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END
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```
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OR
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```
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CASE WHEN condition1 THEN result1
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[WHEN condition2 THEN result2]
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...
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[WHEN conditionN THEN resultN]
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[ELSE result]
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END
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```
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Compare the expression with multiple possible values, and return the corresponding results when matching
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### example
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```
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mysql> select user_id, case user_id when 1 then 'user_id = 1' when 2 then 'user_id = 2' else 'user_id not exist' end test_case from test;
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+---------+-------------+
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| user_id | test_case |
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+---------+-------------+
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| 1 | user_id = 1 |
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| 2 | user_id = 2 |
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+---------+-------------+
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mysql> select user_id, case when user_id = 1 then 'user_id = 1' when user_id = 2 then 'user_id = 2' else 'user_id not exist' end test_case from test;
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+---------+-------------+
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| user_id | test_case |
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+---------+-------------+
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| 1 | user_id = 1 |
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| 2 | user_id = 2 |
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+---------+-------------+
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```
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### keywords
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CASE
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