62 lines
1.3 KiB
Markdown
62 lines
1.3 KiB
Markdown
---
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{
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"title": "nullif",
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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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# nullif
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## description
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### Syntax
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`nullif(expr1, expr2)`
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如果两个参数相等，则返回NULL。否则返回第一个参数的值。它和以下的 `CASE WHEN` 效果一样
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```
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CASE
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WHEN expr1 = expr2 THEN NULL
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ELSE expr1
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END
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```
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## example
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```
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mysql> select nullif(1,1);
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+--------------+
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| nullif(1, 1) |
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+--------------+
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| NULL |
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+--------------+
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mysql> select nullif(1,0);
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+--------------+
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| nullif(1, 0) |
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+--------------+
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| 1 |
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+--------------+
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```
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## keyword
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NULLIF
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