TRIM

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 LEADING、TRAILING 或 BOTH）的规定，从修剪源字符串的开头和/或结尾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重复的修剪字符。如果指定了 TRAILING，则仅删除源字符串末尾重复的修剪字符。如果同时指定了 BOTH，或者完全省略了修剪说明符，则将从源字符串的开头和结尾删除重复项。

如果未明确指定修剪字符，则默认为空格字符 ('')。只允许使用一个修剪字符；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

TRIM(' Trim front and back ')

TRIM (BOTH FROM ' Trim front and back ')

TRIM (BOTH ' ' FROM ' Trim front and back ')

TRIM (LEADING 'x' FROM 'xxxTrim frontxxx')

TRIM (TRAILING 'x' FROM 'xxxTrimxBackxxx')

TRIM (BOTH 'y' FROM 'xxxNo y to trimxxx')