Reference : http://www.cnblogs.com/xiangxiaodong/archive/2011/02/21/1959589.html
使用举例：
select stock_code, concat(substring(date_info, 9, 4), "00") from stock_real order by stock_code;
二，mysql字符串操作函数
1，UPPER和UCASE
返回字符串str，根据当前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改变成大写。该函数对多字节是可靠的。
mysql> select name,UPPER(name) from string_test where name='tank'; +------+-------------+ | name | UPPER(name) | +------+-------------+ | tank | TANK | +------+-------------+ 1 row in set (0.00 sec)
2，LOWER和LCASE
返回字符串str，根据当前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改变成小写。该函数对多字节是可靠的。
mysql> select sex,LCASE(job) from string_test where job='DUCK'; +------+------------+ | sex | LCASE(job) | +------+------------+ | 1 | duck | +------+------------+ 1 row in set (0.00 sec)
3，FIND_IN_SET(str,strlist)
如果字符串str在由N子串组成的表strlist之中，返回一个1到N的值。一个字符串表是被“,”分隔的子串组成的一个字符串。如果第一个参数是一个常数字符串并且第二个参数是一种类型为SET的列，FIND_IN_SET()函数被优化而使用位运算！如果str不是在strlist里面或如果 strlist是空字符串，返回0。如果任何一个参数是NULL，返回NULL。如果第一个参数包含一个“,”，该函数将工作不正常。看面是二种不同的效果，可以看一下
mysql> SELECT id,name FROM string_test WHERE find_in_set('fly',hobby);
+----+-------+
| id | name |
+----+-------+
| 2 | zhang |
+----+-------+
1 row in set (0.00 sec)
mysql> SELECT id,name FROM string_test WHERE hobby like 'fly%';
+----+-------+
| id | name |
+----+-------+
| 2 | zhang |
| 3 | ying |
+----+-------+
2 rows in set (0.00 sec)4，FIELD(str,str1,str2,str3,…)
返回str在str1, str2, str3, …清单的索引。如果str没找到，返回0。FIELD()是ELT()反运算。
mysql> SELECT id, name, FIELD( id, name, sex, job, hobby ) -> FROM string_test where id < 4; +----+-------+------------------------------------+ | id | name | FIELD( id, name, sex, job, hobby ) | +----+-------+------------------------------------+ | 1 | tank | 2 | | 2 | zhang | 0 | | 3 | ying | 0 | +----+-------+------------------------------------+ 3 rows in set (0.00 sec)
5.ELT(N,str1,str2,str3,…)
如果N= 1，返回str1，如果N= 2，返回str2，等等。如果N小于1或大于参数个数，返回NULL。ELT()是FIELD()反运算。
mysql> SELECT id, name, ELT(1, id, name, sex, job, hobby ) FROM string_test where id < 4; +----+-------+------------------------------------+ | id | name | ELT(1, id, name, sex, job, hobby ) | +----+-------+------------------------------------+ | 1 | tank | 1 | | 2 | zhang | 2 | | 3 | ying | 3 | +----+-------+------------------------------------+ 3 rows in set (0.00 sec) mysql> SELECT id, name, ELT(2, id, name, sex, job, hobby ) FROM string_test where id < 4; +----+-------+------------------------------------+ | id | name | ELT(2, id, name, sex, job, hobby ) | +----+-------+------------------------------------+ | 1 | tank | tank | | 2 | zhang | zhang | | 3 | ying | ying | +----+-------+------------------------------------+ 3 rows in set (0.00 sec)
6，REPLACE(str,from_str,to_str)
返回字符串str，其字符串from_str的所有出现由字符串to_str代替。
mysql> SELECT id,REPLACE(hobby,"firend",'living') FROM string_test WHERE id = 2; +----+----------------------------------+ | id | REPLACE(hobby,"firend",'living') | +----+----------------------------------+ | 2 | fly,make living | +----+----------------------------------+ 1 row in set (0.00 sec)
7，REPEAT(str,count)
返回由重复countTimes次的字符串str组成的一个字符串。如果count <= 0，返回一个空字符串。如果str或count是NULL，返回NULL。
mysql> SELECT id,REPEAT(name,2) FROM string_test WHERE id > 1 and id < 4; +----+----------------+ | id | REPEAT(name,2) | +----+----------------+ | 2 | zhangzhang | | 3 | yingying | +----+----------------+ 2 rows in set (0.00 sec)
8，REVERSE(str)
返回颠倒字符顺序的字符串str。
mysql> SELECT id,reverse(name) FROM string_test WHERE id > 1 and id < 4; +----+---------------+ | id | reverse(name) | +----+---------------+ | 2 | gnahz | | 3 | gniy | +----+---------------+ 2 rows in set (0.00 sec)
9，INSERT(str,pos,len,newstr)
返回字符串str，在位置pos起始的子串且len个字符长得子串由字符串newstr代替。
mysql> select id,name,INSERT(hobby,10,6,'living') from string_test where id = 2; +----+-------+-----------------------------+ | id | name | INSERT(hobby,10,6,'living') | +----+-------+-----------------------------+ | 2 | zhang | fly,make living | +----+-------+-----------------------------+ 1 row in set (0.00 sec)
10，SUBSTRING(str FROM pos)
从字符串str的起始位置pos返回一个子串。下面的sub2没有值，因为mysql数据库的下标是从1开始的。
mysql> SELECT id, substring( hobby, 1, 6) AS sub1, substring( hobby from 0 for 8 ) AS sub2,substring( hobby,2) AS sub3, substring( hobby from 4 ) AS sub4 FROM s tring_test WHERE id =4; +----+--------+------+-----------+---------+ | id | sub1 | sub2 | sub3 | sub4 | +----+--------+------+-----------+---------+ | 4 | i love | | love you | ove you | +----+--------+------+-----------+---------+ 1 row in set (0.00 sec)
11,SUBSTRING_INDEX(str,delim,count)
返回从字符串str的第count个出现的分隔符delim之后的子串。如果count是正数，返回最后的分隔符到左边(从左边数) 的所有字符。如果count是负数，返回最后的分隔符到右边的所有字符(从右边数)。
mysql> SELECT id,SUBSTRING_INDEX(hobby,',',2) as test1,SUBSTRING_INDEX(hobby,',' ,-1) as test2 FROM string_test WHERE id = 3; +----+----------------+---------+ | id | test1 | test2 | +----+----------------+---------+ | 3 | flying,driving | testing | +----+----------------+---------+ 1 row in set (0.01 sec)
12,LTRIM(str)
返回删除了其前置空格字符的字符串str。
mysql> SELECT id,LTRIM(job) FROM string_test WHERE id = 4; +----+----------------+ | id | LTRIM(job) | +----+----------------+ | 4 | love your love | +----+----------------+ 1 row in set (0.00 sec)
13,RTRIM(str)
返回删除了其拖后空格字符的字符串str。
mysql> SELECT id,RTRIM(job) FROM string_test WHERE id = 4; +----+----------------+ | id | RTRIM(job) | +----+----------------+ | 4 | love your love | +----+----------------+ 1 row in set (0.00 sec)
14,TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
返回字符串str，其所有remstr前缀或后缀被删除了。如果没有修饰符BOTH、LEADING或TRAILING给出，BOTH被假定。如果remstr没被指定，空格被删除。
mysql> select trim(' test ');
+-----------------+
| trim(' test ') |
+-----------------+
| test |
+-----------------+
1 row in set (0.01 sec)
mysql> SELECT id,TRIM(LEADING "love" from job) as test1,TRIM(BOTH "love" from jo
b) as test2,TRIM(TRAILING "love" from job) as test3 FROM string_test WHERE id =
4
-> ;
+----+------------+--------+------------+
| id | test1 | test2 | test3 |
+----+------------+--------+------------+
| 4 | your love | your | love your |
+----+------------+--------+------------+
1 row in set (0.00 sec)15,MID(str,pos,len)
从字符串str返回一个len个字符的子串，从位置pos开始。使用FROM的变种形式是ANSI SQL92语法。
mysql> SELECT id, mid( hobby, 1, 6 ) AS sub1, mid( hobby -> FROM 0 -> FOR 8 ) AS sub2, mid( hobby, 2 ) AS sub3, mid( hobby -> FROM 4 ) AS sub4 -> FROM string_test -> WHERE id =4 ; +----+--------+------+-----------+---------+ | id | sub1 | sub2 | sub3 | sub4 | +----+--------+------+-----------+---------+ | 4 | i love | | love you | ove you | +----+--------+------+-----------+---------+ 1 row in set (0.00 sec) mysql>
16，LPAD(str,len,padstr)
返回字符串str，左面用字符串padstr填补直到str是len个字符长。
mysql> SELECT id,LPAD(name,11,"zhang ") FROM string_test WHERE id = 3; +----+------------------------+ | id | LPAD(name,11,"zhang ") | +----+------------------------+ | 3 | zhang zying | +----+------------------------+ 1 row in set (0.00 sec)
17,RPAD(str,len,padstr)
返回字符串str，右面用字符串padstr填补直到str是len个字符长。
mysql> SELECT id,RPAD(name,11," ying") FROM string_test WHERE id = 2; +----+-----------------------+ | id | RPAD(name,11," ying") | +----+-----------------------+ | 2 | zhang ying | +----+-----------------------+ 1 row in set (0.00 sec)
18,LEFT(str,len)
返回字符串str的最左面len个字符。
mysql> SELECT id,left(job,4) FROM string_test WHERE id = 4; +----+-------------+ | id | left(job,4) | +----+-------------+ | 4 | love | +----+-------------+ 1 row in set (0.00 sec)
19,RIGHT(str,len)
返回字符串str的最右面len个字符。
mysql> SELECT id,right(job,4) FROM string_test WHERE id = 4; +----+--------------+ | id | right(job,4) | +----+--------------+ | 4 | love | +----+--------------+ 1 row in set (0.00 sec)
20,位置控制函数
POSITION(substr IN str)
返回子串substr在字符串str第一个出现的位置，如果substr不是在str里面，返回0.
LOCATE(substr,str,pos)
返回子串substr在字符串str第一个出现的位置，从位置pos开始。如果substr不是在str里面，返回0。
INSTR(str,substr)
返回子串substr在字符串str中的第一个出现的位置。这与有2个参数形式的LOCATE()相同，除了参数被颠倒。
mysql> SELECT id,INSTR(job,"you") as instr,LOCATE('love',job,3) as locate,POSITI
ON('love' in job) as position FROM string_test WHERE id = 4;
+----+-------+--------+----------+
| id | instr | locate | position |
+----+-------+--------+----------+
| 4 | 6 | 11 | 1 |
+----+-------+--------+----------+
1 row in set (0.00 sec)21，得到字符串长度的函数
LENGTH(str),OCTET_LENGTH(str),CHAR_LENGTH(str),CHARACTER_LENGTH(str)
mysql> SELECT id,LENGTH(job) as one,OCTET_LENGTH(job) as two,CHAR_LENGTH(job) as three,CHARACTER_LENGTH(job) as four FROM string_test WHERE id = 4; +----+-----+-----+-------+------+ | id | one | two | three | four | +----+-----+-----+-------+------+ | 4 | 14 | 14 | 14 | 14 | +----+-----+-----+-------+------+ 1 row in set (0.00 sec)
22，合并多个字符串，或者表中的多个字段
CONCAT(str1,str2,…)
返回来自于参数连结的字符串。如果任何参数是NULL，返回NULL。可以有超过2个的参数。一个数字参数被变换为等价的字符串形式。
mysql> SELECT id,CONCAT(name,job,hobby) FROM string_test WHERE id = 4; +----+-----------------------------------+ | id | CONCAT(name,job,hobby) | +----+-----------------------------------+ | 4 | tankzhanglove your lovei love you | +----+-----------------------------------+ 1 row in set (0.00 sec)
23，进制转换
BIN(N)
返回二进制值N的一个字符串表示，在此N是一个长整数(BIGINT)数字，这等价于CONV(N,10,2)。如果N是NULL，返回NULL。
OCT(N)
返回八进制值N的一个字符串的表示，在此N是一个长整型数字，这等价于CONV(N,10,8)。如果N是NULL，返回NULL。
HEX(N)
返回十六进制值N一个字符串的表示，在此N是一个长整型(BIGINT)数字，这等价于CONV(N,10,16)。如果N是NULL，返回NULL。
ASCII(str)
返回字符串str的最左面字符的ASCII代码值。如果str是空字符串，返回0。如果str是NULL，返回NULL。
mysql> select bin(20),oct(20),hex(20),ascii(20); +---------+---------+---------+-----------+ | bin(20) | oct(20) | hex(20) | ascii(20) | +---------+---------+---------+-----------+ | 10100 | 24 | 14 | 50 | +---------+---------+---------+-----------+ 1 row in set (0.02 sec)
上面我只例举了一部分对字符串进行操作的函数，并且是我觉得我们平时会用的，有可能会用到的一些函数。
