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mysql字符串函数有哪些?

时间:2021-07-01 10:21:17 帮助过:60人阅读

mysql字符串函数有:1、LOWER,将字符串参数值转换为全小写字母后返回;2、UPPER,将字符串参数值转换为全大写字母后返回;3、CONCAT,将多个字符串参数首尾相连后返回;4、SUBSTR,从源字符串str中指定位置pos开始取。

mysql字符串函数有:

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1、LOWER(column|str):将字符串参数值转换为全小写字母后返回

mysql> select lower('SQL Course');+---------------------+
| lower('SQL Course') |
+---------------------+
| sql course          |
+---------------------+

2、UPPER(column|str):将字符串参数值转换为全大写字母后返回

mysql> select upper('Use MYsql');+--------------------+
| upper('Use MYsql') |
+--------------------+
| USE MYSQL          |
+--------------------+

3、CONCAT(column|str1, column|str2,...):将多个字符串参数首尾相连后返回

mysql> select concat('My','S','QL');+-----------------------+
| concat('My','S','QL') |
+-----------------------+
| MySQL                 |
+-----------------------+

如果有任何参数为null,则函数返回null

mysql> select concat('My',null,'QL');+------------------------+
| concat('My',null,'QL') |
+------------------------+
| NULL                   |
+------------------------+

如果参数是数字,则自动转换为字符串

mysql> select concat(14.3,'mysql');+----------------------+
| concat(14.3,'mysql') |
+----------------------+
| 14.3mysql            |
+----------------------+

4、CONCAT_WS(separator,str1,str2,...):将多个字符串参数以给定的分隔符separator首尾相连后返回

mysql> select concat_ws(';','First name','Second name','Last name');+-------------------------------------------------------+
| concat_ws(';','First name','Second name','Last name') |
+-------------------------------------------------------+
| First name;Second name;Last name                      |
+-------------------------------------------------------+

!!也就是函数圆括号里的第一个项目用来指定分隔符

5、SUBSTR(str,pos[,len]):从源字符串str中的指定位置pos开始取一个字串并返回

注意:

  ①len指定子串的长度,如果省略则一直取到字符串的末尾;len为负值表示从源字符串的尾部开始取起。

  ②函数SUBSTR()是函数SUBSTRING()的同义词。

mysql> select substring('hello world',5);+----------------------------+
| substring('hello world',5) |
+----------------------------+
| o world                    |
+----------------------------+mysql> select substr('hello world',5,3);+---------------------------+
| substr('hello world',5,3) |
+---------------------------+
| o w                       |
+---------------------------+mysql> select substr('hello world',-5);+--------------------------+
| substr('hello world',-5) |
+--------------------------+
| world                    |
+--------------------------+

6、LENGTH(str):返回字符串的存储长度

mysql> select length('text'),length('你好');+----------------+------------------+
| length('text') | length('你好')   |
+----------------+------------------+
|              4 |                6 |
+----------------+------------------+

注意:编码方式不同字符串的存储长度就不一样(‘你好’:utf8是6,gbk是4)

7、CHAR_LENGTH(str):返回字符串中的字符个数

mysql> select char_length('text'),char_length('你好');+---------------------+-----------------------+
| char_length('text') | char_length('你好')   |
+---------------------+-----------------------+
|                   4 |                     2 |
+---------------------+-----------------------+

8、INSTR(str, substr):从源字符串str中返回子串substr第一次出现的位置

mysql> select instr('foobarbar','bar');+--------------------------+
| instr('foobarbar','bar') |
+--------------------------+
|                        4 |
+--------------------------+

9、LPAD(str, len, padstr):在源字符串的左边填充给定的字符padstr到指定的长度len,返回填充后的字符串

mysql> select lpad('hi',5,'??');+-------------------+
| lpad('hi',5,'??') |
+-------------------+
| ???hi             |
+-------------------+

10、RPAD(str, len, padstr):在源字符串的右边填充给定的字符padstr到指定的长度len,返回填充后的字符串

mysql> select rpad('hi',6,'??');+-------------------+| rpad('hi',6,'??') |+-------------------+| hi????            |+-------------------+


11、TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str):

从源字符串str中去掉两端、前缀或后缀字符remstr并返回;

  如果不指定remstr,则去掉str两端的空格;不指定BOTH、LEADING、TRAILING ,则默认为 BOTH。

mysql> select trim('  bar  ');+-----------------+
| trim('  bar  ') |
+-----------------+
| bar             |
+-----------------+mysql> select trim(leading 'x' from 'xxxbarxxx');+------------------------------------+
| trim(leading 'x' from 'xxxbarxxx') |
+------------------------------------+
| barxxx                             |
+------------------------------------+mysql> select trim(both 'x' from 'xxxbarxxx');+---------------------------------+
| trim(both 'x' from 'xxxbarxxx') |
+---------------------------------+
| bar                             |
+---------------------------------+mysql> select trim(trailing 'xyz' from 'barxxyz');+-------------------------------------+
| trim(trailing 'xyz' from 'barxxyz') |
+-------------------------------------+
| barx                                |
+-------------------------------------+

12、REPLACE(str, from_str, to_str):在源字符串str中查找所有的子串form_str(大小写敏感),找到后使用替代字符串to_str替换它。返回替换后的字符串

mysql> select replace('www.mysql.com','w','Ww');+-----------------------------------+
| replace('www.mysql.com','w','Ww') |
+-----------------------------------+
| WwWwWw.mysql.com                  |
+-----------------------------------+

13、LTRIM(str),RTRIM(str):去掉字符串的左边或右边的空格(左对齐、右对齐)

mysql> SELECT  ltrim('   barbar   ') rs1, rtrim('   barbar   ') rs2;+-----------+-----------+
| rs1       | rs2       |
+-----------+-----------+
| barbar    |    barbar |
+-----------+-----------+

14、REPEAT(str, count):将字符串str重复count次后返回

mysql> select repeat('MySQL',3);+-------------------+
| repeat('MySQL',3) |
+-------------------+
| MySQLMySQLMySQL   |
+-------------------+

15、REVERSE(str):将字符串str反转后返回

mysql> select reverse('abcdef');+-------------------+
| reverse('abcdef') |
+-------------------+
| fedcba            |
+-------------------+

16、CHAR(N,... [USING charset_name]):将每个参数N解释为整数(字符的编码),并返回每个整数对应的字符所构成的字符串(NULL值被忽略)。

mysql> select char(77,121,83,81,'76'),char(77,77.3,'77.3');+-------------------------+----------------------+
| char(77,121,83,81,'76') | char(77,77.3,'77.3') |
+-------------------------+----------------------+
| MySQL                   | MMM                  |
+-------------------------+----------------------+

默认情况下,函数返回二进制字符串,若想返回针对特定字符集的字符串,使用using选项

mysql> SELECT charset(char(0x65)), charset(char(0x65 USING utf8));+---------------------+--------------------------------+
| charset(char(0x65)) | charset(char(0x65 USING utf8)) |
+---------------------+--------------------------------+
| binary              | utf8                           |
+---------------------+--------------------------------+

17、FORMAT(X,D[,locale]):以格式‘#,###,###.##’格式化数字X

  • D指定小数位数

  • locale指定国家语言(默认的locale为en_US)

mysql> SELECT format(12332.123456, 4),format(12332.2,0);+-------------------------+-------------------+
| format(12332.123456, 4) | format(12332.2,0) |
+-------------------------+-------------------+
| 12,332.1235 | 12,332 |
+-------------------------+-------------------+mysql> SELECT format(12332.2,2,'de_DE');+---------------------------+
| format(12332.2,2,'de_DE') |
+---------------------------+
| 12.332,20 |
+---------------------------+

18、SPACE(N):返回由N个空格构成的字符串

mysql> select space(3);+----------+
| space(3) |
+----------+
|          |
+----------+

19、LEFT(str, len):返回最左边的len长度的子串

mysql> select left('chinaitsoft',5);+-----------------------+
| left('chinaitsoft',5) |
+-----------------------+
| china                 |
+-----------------------+

20、RIGHT(str, len):返回最右边的len长度的子串

mysql> select right('chinaitsoft',5);+------------------------+
| right('chinaitsoft',5) |
+------------------------+
| tsoft                  |
+------------------------+

21、STRCMP(expr1,expr2):如果两个字符串是一样的则返回0;如果第一个小于第二个则返回-1;否则返回1

mysql> select strcmp('text','text');+-----------------------+
| strcmp('text','text') |
+-----------------------+
|                     0 |
+-----------------------+mysql> SELECT strcmp('text', 'text2'),strcmp('text2', 'text');+-------------------------+-------------------------+
| strcmp('text', 'text2') | strcmp('text2', 'text') |
+-------------------------+-------------------------+
|                      -1 |                       1 |
+-------------------------+-------------------------+

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