---
{
    "title": "case",
    "language": "en"
}
---

<!-- 
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you 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.
-->

# case
## description
### Syntax

```
CASE expression
    WHEN condition1 THEN result1
    [WHEN condition2 THEN result2]
    ...
    [WHEN conditionN THEN resultN]
    [ELSE result]
END
```
OR
```
CASE WHEN condition1 THEN result1
    [WHEN condition2 THEN result2]
    ...
    [WHEN conditionN THEN resultN]
    [ELSE result]
END
```

Compare the expression with multiple possible values, and return the corresponding results when matching

## example

```
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;
+---------+-------------+
| user_id | test_case   |
+---------+-------------+
| 1       | user_id = 1 |
| 2       | user_id = 2 |
+---------+-------------+
 
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;
+---------+-------------+
| user_id | test_case   |
+---------+-------------+
| 1       | user_id = 1 |
| 2       | user_id = 2 |
+---------+-------------+
```
## keyword
CASE