mysql count转字符串_MySQL字符串函数

把字符串转成小写

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)

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> SELECTid, 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 FROMs

tring_testWHERE id =4;+----+--------+------+-----------+---------+

| id | sub1 | sub2 | sub3 | sub4 |

+----+--------+------+-----------+---------+

+----+--------+------+-----------+---------+

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" fromjo

b)as test2,TRIM(TRAILING "love" from job) as test3 FROM string_test WHERE id =

->;+----+------------+--------+------------+

+----+------------+--------+------------+

+----+------------+--------+------------+

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 ) ASsub1, mid( hobby-> FROM 0

-> FOR 8 ) AS sub2, mid( hobby, 2 ) ASsub3, mid( hobby-> FROM 4 ) ASsub4-> FROMstring_test-> WHERE id =4;+----+--------+------+-----------+---------+

| id | sub1 | sub2 | sub3 | sub4 |

+----+--------+------+-----------+---------+

+----+--------+------+-----------+---------+

1 row in set (0.00 sec)

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) aslocate,POSITION('love' in job) as position FROM string_test WHERE id = 4;+----+-------+--------+----------+

+----+-------+--------+----------+

| 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) asthree,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。

在MySQL中进行字符串的拼接要使用CONCAT()函数，CONCAT()函数支持一个或者多个参数，参数类型可以为字符串类型也可以是非字符串类型。对于非字符串类型的参数MySQL将尝试将其转化为字符串类型，CONCAT()函数会将所有参数按照参数的顺序拼接成一个字符串作为返回值。比如下面的SQL语句用于将用户的多个字段信息以一个字段的形式查询出来：

SELECT CONCAT('Staff Number :', 'Happiness Index', FNumber, FSalary/(FAge-21)) fromt_employee+----------------------------------------------------------+

| concat |

+----------------------------------------------------------+

| Staff number: Happiness index of DEV001 is 2075.000000 |

| Staff number: Happiness index of DEV002 is 328.571429 |

| NULL |

| Staff number: Happiness index of HR001 is 2150.000000 |

| Staff number: Happiness index of HR002 is 825.000000 |

| Staff number: Happiness index of IT001 is 785.714286 |

| Staff number: Happiness index of IT002 is 466.666667 |

| Staff number: Happiness index of SALES001 is 1325.000000 |

| Staff number: Happiness index of SALES002 is 592.857143 |

+----------------------------------------------------------+