Mysql函数总结（1）——字符串函数

1. ASCII(str)
说明：返回str第一个字符的ASCII码；如果str为空，则返回0；如果str为NULL，则返回NULL。
示例：
mysql> select ascii('name');
+---------------+
| ascii('name') |
+---------------+
|           110 |
+---------------+
1 row in set (0.00 sec)

mysql> select ascii('');
+-----------+
| ascii('') |
+-----------+
|         0 |
+-----------+
1 row in set (0.00 sec)

mysql> select ascii(NULL);
+-------------+
| ascii(NULL) |
+-------------+
|        NULL |
+-------------+
1 row in set (0.00 sec)

mysql>

2. BIN(N)
说明：返回N的二进制值的字符串标示，N为BIGINT类型。如果N为NULL，则返回NULL。
示例：
mysql> select bin(100);
+----------+
| bin(100) |
+----------+
| 1100100  |
+----------+
1 row in set (0.00 sec)

mysql>

3.BIN_LENGTH(str)
说明：返回字符串str的长度，单位为BIT。
示例：
mysql> select bit_length('name');
+--------------------+
| bit_length('name') |
+--------------------+
|                 32 |
+--------------------+
1 row in set (0.00 sec)

mysql>

4.CHAR(N1, N2 ... [USING charset_name])
说明：返回由整数N1,N2,...组成的字符串。
示例：
mysql> SELECT CHAR(77,121,83,81,'76');
+-------------------------+
| CHAR(77,121,83,81,'76') |
+-------------------------+
| MySQL                   |
+-------------------------+
1 row in set (0.00 sec)

mysql> select char(77, 77.3, 77.6);
+----------------------+
| char(77, 77.3, 77.6) |
+----------------------+
| MMN                  |
+----------------------+
1 row in set (0.00 sec)

mysql>

5.CHAR_LENGTH(str)
说明：返回字符串str的长度，单位为character。
示例：
mysql> select char_length('name');
+---------------------+
| char_length('name') |
+---------------------+
|                   4 |
+---------------------+
1 row in set (0.00 sec)

mysql>

6.CHARACTER_LENGTH(str)
说明：同CHAR_LENGTH(str)

7.CONCAT(str1,str2,...)
说明：字符串拼接。如果其中任何一个字符串为NULL，则返回NULL
示例：
mysql> select concat('Hello', ' ', 'Mysql');
+-------------------------------+
| concat('Hello', ' ', 'Mysql') |
+-------------------------------+
| Hello Mysql                   |
+-------------------------------+
1 row in set (0.00 sec)

mysql> select concat('Hello', ' ', 'Mysql', NULL);
+-------------------------------------+
| concat('Hello', ' ', 'Mysql', NULL) |
+-------------------------------------+
| NULL                                |
+-------------------------------------+
1 row in set (0.00 sec)

mysql>

8.CONCAT_WS(separator,str1,str2,...)
说明：字符串拼接。以sepatator作为分隔符。CONCAT_WS意为Concatenate With Separator。如果separator为NULL，则结果为NULL。
示例：
mysql> select concat_ws(' ', 'Hello', 'Mysql');
+----------------------------------+
| concat_ws(' ', 'Hello', 'Mysql') |
+----------------------------------+
| Hello Mysql                      |
+----------------------------------+
1 row in set (0.00 sec)

mysql>

9. ELT(N,str1,str2,str3,...)
说明：返回str1,str2,str3,...中的第N个字符串。
示例：
mysql> SELECT ELT(1, 'ej', 'Heja', 'hej', 'foo');
+------------------------------------+
| ELT(1, 'ej', 'Heja', 'hej', 'foo') |
+------------------------------------+
| ej                                 |
+------------------------------------+
1 row in set (0.02 sec)

mysql> SELECT ELT(4, 'ej', 'Heja', 'hej', 'foo');
+------------------------------------+
| ELT(4, 'ej', 'Heja', 'hej', 'foo') |
+------------------------------------+
| foo                                |
+------------------------------------+
1 row in set (0.00 sec)

mysql>

10.EXPORT_SET(bits,on,off[,separator[,number_of_bits]])
说明：从低到高以此检查bits的各个bit位。如果该位为1，则输出on；如果该位为0，则输出off。separator为输出分隔符，默认为逗号。number_of_bits为需要检查的位数，默认为64
示例：
mysql> select export_set(13, 'yes', 'no', ',', 4);
+-------------------------------------+
| export_set(13, 'yes', 'no', ',', 4) |
+-------------------------------------+
| yes,no,yes,yes                      |
+-------------------------------------+
1 row in set (0.00 sec)

mysql> select export_set(0b1101, 'yes', 'no', ',', 4);
+-----------------------------------------+
| export_set(0b1101, 'yes', 'no', ',', 4) |
+-----------------------------------------+
| yes,no,yes,yes                          |
+-----------------------------------------+
1 row in set (0.00 sec)

mysql>

11.FIELD(str,str1,str2,str3,...)
说明：返回str在str1,str2,str3,...中的位置。如果没找到str，则返回0
示例：
mysql> select field('a', 'a', 'b', 'c');
+---------------------------+
| field('a', 'a', 'b', 'c') |
+---------------------------+
|                         1 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select field('d', 'a', 'b', 'c');
+---------------------------+
| field('d', 'a', 'b', 'c') |
+---------------------------+
|                         0 |
+---------------------------+
1 row in set (0.00 sec)

mysql>

12.FORMAT(X,D[,locale])
说明：将X格式化为'#,###,###.##'的字符串，d为保留的小数位数
示例：
mysql> SELECT FORMAT(12332.123456, 4);
+-------------------------+
| FORMAT(12332.123456, 4) |
+-------------------------+
| 12,332.1235             |
+-------------------------+
1 row in set (0.00 sec)

mysql>

13.HEX(str),HEX(N)
说明：
HEX(str)返回对字符串str的十六进制表示
HEX(N)返回对整数N的十六进制字符串表示
mysql> select hex('Mysql'), hex(255);
+--------------+----------+
| hex('Mysql') | hex(255) |
+--------------+----------+
| 4D7973716C   | FF       |
+--------------+----------+
1 row in set (0.00 sec)

mysql>

14.INSERT(str,pos,len,newstr)
说明：将str中pos开始，长度为len的字符串替换为newstr，返回新字符串。如果pos越界，则返回str；如果len越界，则替换从pos开始的所有字符串。
示例：
mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
+-----------------------------------+
| INSERT('Quadratic', 3, 4, 'What') |
+-----------------------------------+
| QuWhattic                         |
+-----------------------------------+
1 row in set (0.03 sec)

mysql> SELECT INSERT('Quadratic', -1, 4, 'What');
+------------------------------------+
| INSERT('Quadratic', -1, 4, 'What') |
+------------------------------------+
| Quadratic                          |
+------------------------------------+
1 row in set (0.06 sec)

mysql> SELECT INSERT('Quadratic', 3, 100, 'What');
+-------------------------------------+
| INSERT('Quadratic', 3, 100, 'What') |
+-------------------------------------+
| QuWhat                              |
+-------------------------------------+
1 row in set (0.00 sec)

mysql>

15.INSTR(str,substr)
说明：返回子字符串substr在str中的位置。如果不存在，则返回0。
示例：
mysql> SELECT INSTR('foobarbar', 'bar');
+---------------------------+
| INSTR('foobarbar', 'bar') |
+---------------------------+
|                         4 |
+---------------------------+
1 row in set (0.08 sec)

mysql> SELECT INSTR('xbar', 'foobar');
+-------------------------+
| INSTR('xbar', 'foobar') |
+-------------------------+
|                       0 |
+-------------------------+
1 row in set (0.00 sec)

mysql>

16.LEFT(str,len)
说明：返回str左端的len个字符
示例：
mysql> SELECT LEFT('foobarbar', 5);
+----------------------+
| LEFT('foobarbar', 5) |
+----------------------+
| fooba                |
+----------------------+
1 row in set (0.00 sec)

mysql>

17. LENGTH(str)
说明：返回字符串str的长度，以字节为单位。
示例：
mysql> SELECT LENGTH('text');
+----------------+
| LENGTH('text') |
+----------------+
|              4 |
+----------------+
1 row in set (0.00 sec)

mysql>

18. LOCATE(substr,str), LOCATE(substr,str,pos)
说明：类似于INSTR(str,substr)，区别是两个字符串的位置相反。pos表示开始查找的位置。如果没有，则返回0
示例：
mysql> SELECT LOCATE('bar', 'foobarbar');
+----------------------------+
| LOCATE('bar', 'foobarbar') |
+----------------------------+
|                          4 |
+----------------------------+
1 row in set (0.00 sec)

mysql> SELECT LOCATE('xbar', 'foobar');
+--------------------------+
| LOCATE('xbar', 'foobar') |
+--------------------------+
|                        0 |
+--------------------------+
1 row in set (0.00 sec)

mysql> SELECT LOCATE('bar', 'foobarbar', 5);
+-------------------------------+
| LOCATE('bar', 'foobarbar', 5) |
+-------------------------------+
|                             7 |
+-------------------------------+
1 row in set (0.00 sec)

mysql>

19.LOWER(str)
说明：返回字符串str的小写
示例：
mysql> SELECT LOWER('QUADRATICALLY');
+------------------------+
| LOWER('QUADRATICALLY') |
+------------------------+
| quadratically          |
+------------------------+
1 row in set (0.00 sec)

mysql>

20. LPAD(str,len,padstr)
说明：使用padstr对str左端进行补齐，使其长度为len。如果str长度大于len，则将str截断为len返回。
示例：
mysql> SELECT LPAD('hi',4,'??');
+-------------------+
| LPAD('hi',4,'??') |
+-------------------+
| ??hi              |
+-------------------+
1 row in set (0.00 sec)

mysql> SELECT LPAD('hi',1,'??');
+-------------------+
| LPAD('hi',1,'??') |
+-------------------+
| h                 |
+-------------------+
1 row in set (0.00 sec)

mysql>

21.LTRIM(str)
说明：去掉str左端的空白字符
示例：
mysql> SELECT LTRIM(' barbar');
+------------------+
| LTRIM(' barbar') |
+------------------+
| barbar           |
+------------------+
1 row in set (0.02 sec)

mysql>

22.MAKE_SET(bits,str1,str2,...)
说明：根据bits中的位数，使用str1,str2,...来构造字符串集合。
示例：
mysql> SELECT MAKE_SET(1,'a','b','c');
+-------------------------+
| MAKE_SET(1,'a','b','c') |
+-------------------------+
| a                       |
+-------------------------+
1 row in set (0.02 sec)

mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
+----------------------------------------+
| MAKE_SET(1 | 4,'hello','nice','world') |
+----------------------------------------+
| hello,world                            |
+----------------------------------------+
1 row in set (0.04 sec)

mysql>

23.OCT(N)
说明：返回数字N的八进制字符串表示
示例：
mysql> SELECT OCT(12);
+---------+
| OCT(12) |
+---------+
| 14      |
+---------+
1 row in set (0.00 sec)

mysql>

24. REPEAT(str,count)
说明：将字符串str重复count次返回
示例：
mysql> SELECT REPEAT('MySQL', 3);
+--------------------+
| REPEAT('MySQL', 3) |
+--------------------+
| MySQLMySQLMySQL    |
+--------------------+
1 row in set (0.00 sec)

mysql>

25.REPLACE(str,from_str,to_str)
说明：将字符串str中的所有子字符串from_str替换为to_str
示例：
mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
+-------------------------------------+
| REPLACE('www.mysql.com', 'w', 'Ww') |
+-------------------------------------+
| WwWwWw.mysql.com                    |
+-------------------------------------+
1 row in set (0.02 sec)

mysql>

26.REVERSE(str)
说明：逆序输出字符串str
示例：
mysql> SELECT REVERSE('abc');
+----------------+
| REVERSE('abc') |
+----------------+
| cba            |
+----------------+
1 row in set (0.00 sec)

mysql>

27.RIGHT(str,len)
说明：返回字符串str的右边len个字符
示例：
mysql> SELECT RIGHT('foobarbar', 4);
+-----------------------+
| RIGHT('foobarbar', 4) |
+-----------------------+
| rbar                  |
+-----------------------+
1 row in set (0.00 sec)

mysql>

28.RPAD(str,len,padstr)
说明：使用padstr对str右端进行补齐，使其长度为len。如果str长度大于len，则将str截断为len返回。
示例：
mysql> SELECT RPAD('hi',5,'?');
+------------------+
| RPAD('hi',5,'?') |
+------------------+
| hi???            |
+------------------+
1 row in set (0.00 sec)

mysql> SELECT RPAD('hi',1,'?');
+------------------+
| RPAD('hi',1,'?') |
+------------------+
| h                |
+------------------+
1 row in set (0.00 sec)

mysql>

29.RTRIM(str)
说明：去掉str右端的空白字符
示例：
mysql> SELECT RTRIM('barbar ');
+------------------+
| RTRIM('barbar ') |
+------------------+
| barbar           |
+------------------+
1 row in set (0.00 sec)

mysql>

30.SPACE(N)
说明：返回有N个空白字符组成的字符串
示例：
mysql> SELECT SPACE(6);
+----------+
| SPACE(6) |
+----------+
|          |
+----------+
1 row in set (0.00 sec)

mysql>

31.SUBSTRING(str,pos), SUBSTRING(str FROM pos),SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len)
说明：返回str中从pos开始，长度为len个字符的子字符串。如果pos为负值，则从右端开始计算
示例：
mysql> SELECT SUBSTRING('Quadratically',5,6);
+--------------------------------+
| SUBSTRING('Quadratically',5,6) |
+--------------------------------+
| ratica                         |
+--------------------------------+
1 row in set (0.00 sec)

mysql> SELECT SUBSTRING('Sakila', -5, 3);
+----------------------------+
| SUBSTRING('Sakila', -5, 3) |
+----------------------------+
| aki                        |
+----------------------------+
1 row in set (0.00 sec)

mysql>

32.SUBSTRING_INDEX(str,delim,count)
说明：返回在str中，delim出现count次之前的所有字符串。如果count为负值，则从右端开始查找
示例：
mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);
+------------------------------------------+
| SUBSTRING_INDEX('www.mysql.com', '.', 2) |
+------------------------------------------+
| www.mysql                                |
+------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);
+-------------------------------------------+
| SUBSTRING_INDEX('www.mysql.com', '.', -2) |
+-------------------------------------------+
| mysql.com                                 |
+-------------------------------------------+
1 row in set (0.00 sec)

mysql>

33.TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str)
说明：从str中删除指定位置的remstr字符串。如果不指定remstr，则默认为空白字符。如果不指定位置，则默认为BOTH。
示例：
mysql> SELECT TRIM(' bar ');
+---------------+
| TRIM(' bar ') |
+---------------+
| bar           |
+---------------+
1 row in set (0.02 sec)

mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
+------------------------------------+
| TRIM(LEADING 'x' FROM 'xxxbarxxx') |
+------------------------------------+
| barxxx                             |
+------------------------------------+
1 row in set (0.02 sec)

mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
+---------------------------------+
| TRIM(BOTH 'x' FROM 'xxxbarxxx') |
+---------------------------------+
| bar                             |
+---------------------------------+
1 row in set (0.00 sec)

mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
+-------------------------------------+
| TRIM(TRAILING 'xyz' FROM 'barxxyz') |
+-------------------------------------+
| barx                                |
+-------------------------------------+
1 row in set (0.02 sec)

mysql>

34. UNHEX(str)
说明：将str作为十六进制字符，返回其对应的字符串
示例：
mysql> SELECT UNHEX('4D7953514C');
+---------------------+
| UNHEX('4D7953514C') |
+---------------------+
| MySQL               |
+---------------------+
1 row in set (0.00 sec)

mysql>

35.UPPER(str)
说明：返回字符串str的大写形式
示例：
mysql> SELECT UPPER('Hej');
+--------------+
| UPPER('Hej') |
+--------------+
| HEJ          |
+--------------+
1 row in set (0.00 sec)

mysql>

36.STRCMP(expr1,expr2)
说明：字符串比较
示例：
mysql> SELECT STRCMP('text', 'text2');
+-------------------------+
| STRCMP('text', 'text2') |
+-------------------------+
|                      -1 |
+-------------------------+
1 row in set (0.06 sec)

mysql> SELECT STRCMP('text2', 'text');
+-------------------------+
| STRCMP('text2', 'text') |
+-------------------------+
|                       1 |
+-------------------------+
1 row in set (0.00 sec)

mysql> SELECT STRCMP('text', 'text');
+------------------------+
| STRCMP('text', 'text') |
+------------------------+
|                      0 |
+------------------------+
1 row in set (0.00 sec)

mysql>