1. 替换字符串中的某一个子串
postgres=# select replace('you are a man,old man','man','woman');
you are a woman,old woman
postgres=# select translate('you are a man,'woman');
you ore o wom,old wom
可以看出，translate把替换后的子串截断成原来的子串的长度。
2. trim相关的函数，消除两边的指定子串
> 替换两头的子串：
postgres=# select trim('xxxytrimyyyx','xy');
trim
postgres=# select trim(both 'xy' from 'xxxytrimyyyx'); trim
postgres=# select btrim('xxxytrimyyyx','xy');
trim
> 替换左边的子串
postgres=# select ltrim('xxxytrimyyyx','xy');
trimyyyx
postgres=# select trim(leading 'xy' from 'xxxytrimyyyx');
trimyyyx
> 替换右边的子串
postgres=# select rtrim('xxxytrimyyyx','xy');
xxxytrim
postgres=# select trim(trailing 'xy' from 'xxxytrimyyyx');
xxxytrim
3.抽取字符串
postgres=# select substring('helloworld',2,4);
ello
postgres=# select substr('helloworld',4);
ello
参考地址： http://www.cnblogs.com/stephen-liu74/archive/2012/05/02/2294071.html 原文链接：https://www.f2er.com/postgresql/195411.html
