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# TRIM
<a name="sql-reference-trim"></a>

```
TRIM ( [ [ <trim-specification> ] [ <trim-character> ] FROM ] <trim-source> )
 <trim-specification> := LEADING | TRAILING | BOTH
 <trim-character> := <character-expression>
 <trim-source> := <character-expression>
```



TRIM 根据修剪规范（即前导、 and/or 尾随或两者）的规定，从修剪源字符串的开头端删除指定修剪字符的实例。如果指定了 LEADING，则仅删除源字符串开头处的重复剪裁字符。如果指定了 TRAILING，则仅删除源字符串结尾处的重复剪裁字符。如果指定了 BOTH，或者完全省略了剪裁说明符，则会从源字符串开头和结尾删除重复项。

如果未明确指定剪裁字符，则默认为空格字符 (' ')。只允许使用一个剪裁字符；指定空字符串或长度超过一个字符的字符串会导致异常。

如果任一输入为 null，则返回 null。

## 示例
<a name="sql-reference-trim-examples"></a>


| 函数 | 结果 | 
| --- | --- | 
|  <pre>TRIM(' Trim front and back ')</pre>  |  'Trim front and back'  | 
|  <pre>TRIM (BOTH FROM ' Trim front and back ')</pre>  |  'Trim front and back'  | 
|  <pre>TRIM (BOTH ' ' FROM ' Trim front and back ')</pre>  |  'Trim front and back'  | 
|  <pre>TRIM (LEADING 'x' FROM 'xxxTrim frontxxx')</pre>  |  'Trim frontxxx'  | 
|  <pre>TRIM (TRAILING 'x' FROM 'xxxTrimxBackxxx')</pre>  |  'xxxTrimxBack'  | 
|  <pre>TRIM (BOTH 'y' FROM 'xxxNo y to trimxxx')</pre>  |  'xxxNo y to trimxxx'  |