Postgresql里面内置了很多的实用函数，下面介绍下组合和切割函数
环境：PostgreSQL 9.1.2 CENTOS 5.7 final一.组合函数
1.concat a.语法介绍concat(str "any" [, str "any" [, ...]])Concatenate all but first arguments with separators.The first parameter is used as a separator. NULL arguments are ignored.
b.实际例子:
postgres=# create table t_kenyon(id int,name varchar(10),remark text);CREATE TABLEpostgres=# insert into t_kenyon values(1,'test','kenyon'),(2,'just','china'),(3,'iam','lovingU');INSERT 0 3postgres=# insert into t_kenyon values(4,'test',null);INSERT 0 1postgres=# insert into t_kenyon values(5,null,'adele');INSERT 0 1postgres=# select * from t_kenyon; id | name | remark ----+------+--------- 1 | test | kenyon 2 | just | china 3 | iam | lovingU 4 | test | 5 | | adele(5 rows)postgres=# select concat(id,name,remark) from t_kenyon; concat ------------- 1testkenyon 2justchina 3iamlovingU 4test 5adele(5 rows)
c.说明
concat函数纯粹是一个拼接函数，可以忽略null值拼接，拼接的值没有分隔符，如果需要分割符，则需要用下面的函数concat_ws。2.concat_ws
a.语法介绍concat_ws(sep text, str "any" [, str "any" [,...] ])Concatenate all but first arguments with separators.The first parameter is used as a separator.NULL arguments are ignored.
b.实际应用
postgres=# select concat_ws(',',id,name,remark) from t_kenyon; concat_ws --------------- 1,test,kenyon 2,just,china 3,iam,lovingU 4,test 5,adele(5 rows)postgres=# select concat_ws('_',id,name,remark) from t_kenyon; concat_ws --------------- 1_test_kenyon 2_just_china 3_iam_lovingU 4_test 5_adele(5 rows)postgres=# select concat_ws('',id,name,remark) from t_kenyon; concat_ws ------------- 1testkenyon 2justchina 3iamlovingU 4test 5adele(5 rows)postgres=# select concat_ws('^_*',id,name,remark) from t_kenyon; concat_ws ------------------- 1^_*test^_*kenyon 2^_*just^_*china 3^_*iam^_*lovingU 4^_*test 5^_*adele(5 rows) c.说明 concat_ws函数比concat函数多了分隔符的功能，其实就是concat的升级版，假如分隔符为'',则取出来的结果和concat是一样的。concat_ws分隔符还支持多个字符作为分隔符的，日常用得更多的可能是||。
二、切割函数
1.split_part a.语法介绍split_part(string text, delimiter text, field int)Split string on delimiter and return the given field (counting from one)
b.实际例子
postgres=# select split_part('abc~@~def~@~ghi','~@~', 2); split_part ------------ def(1 row)postgres=# select split_part('now|year|month','|',3); split_part ------------ month(1 row) c.说明
该函数对按分隔符去取某个特定位置上的值非常有效果2.regexp_split_to_table
a.语法介绍regexp_split_to_table(string text, pattern text [, flags text])Split string using a POSIX regular expression as the delimiter.
b.使用例子
postgres=# SELECT regexp_split_to_table('kenyon,love,,china,!',','); regexp_split_to_table ----------------------- kenyon love china !(5 rows)--按分割符切割postgres=# SELECT regexp_split_to_table('kenyon, china loves',E'\\s'); regexp_split_to_table ----------------------- kenyon, china loves(3 rows)--按字母切割postgres=# SELECT regexp_split_to_table('kenyon,,china',E'\\s*'); regexp_split_to_table ----------------------- k e n y o n , , c h i n a(13 rows) 3.regexp_split_to_array
a.语法介绍regexp_split_to_array(string text, pattern text [, flags text ])Split string using a POSIX regular expression as the delimiter.
b.实际例子
postgres=# SELECT regexp_split_to_array('kenyon,love,,china,!',','); regexp_split_to_array -------------------------- {kenyon,love,"",china,!}(1 row)postgres=# SELECT regexp_split_to_array('kenyon,love,,china!','s*'); regexp_split_to_array ----------------------------------------------- {k,e,n,y,o,n,",",l,o,v,e,",",",",c,h,i,n,a,!}(1 row) c.说明
上面用到的flag里的s*表示split all，E'\s'表示转义空格