字符串函數
是最常用的的一種函數,在一個具體應用中通常會綜合幾個甚至幾類函數來實現相應的應用:
1、LOWER(column|str):將字符串參數值轉換為全小寫字母后返回
mysql> select lower('SQL Course'); +---------------------+
| lower('SQL Course') |
+---------------------+
| sql course |
+---------------------+
2、UPPER(column|str):將字符串參數值轉換為全大寫字母后返回
mysql> select upper('Use MYsql'); +--------------------+
| upper('Use MYsql') |
+--------------------+
| USE MYSQL |
+--------------------+
3、CONCAT(column|str1, column|str2,...):將多個字符串參數首尾相連后返回
mysql> select concat('My','S','QL'); +-----------------------+
| concat('My','S','QL') |
+-----------------------+
| MySQL |
+-----------------------+
如果有任何參數為null,則函數返回null
mysql> select concat('My',null,'QL'); +------------------------+
| concat('My',null,'QL') |
+------------------------+
| NULL |
+------------------------+
如果參數是數字,則自動轉換為字符串
mysql> select concat(14.3,'mysql'); +----------------------+
| concat(14.3,'mysql') |
+----------------------+
| 14.3mysql |
+----------------------+
4、CONCAT_WS(separator,str1,str2,...):將多個字符串參數以給定的分隔符separator首尾相連后返回
mysql> select concat_ws(';','First name','Second name','Last name'); +-------------------------------------------------------+
| concat_ws(';','First name','Second name','Last name') |
+-------------------------------------------------------+
| First name;Second name;Last name |
+-------------------------------------------------------+
!!也就是函數圓括號里的第一個項目用來指定分隔符
注意:如果有任何參數為null,則函數不返回null,而是直接忽略它
mysql> select concat_ws(',','id',null,'name'); +---------------------------------+
| concat_ws(',','id',null,'name') |
+---------------------------------+
| id,name |
+---------------------------------+
打開和關閉管道符號“|”的連接功能
PIPES_AS_CONCAT:將“||”視為字符串的連接操作符而非或運算符
|| 管道連接符:
基本格式:
mysql> select 列名1 || 列名2 || 列名3 from 表名;
在mysql中,進行上式連接查詢之后,會將查詢結果集在一列中顯示(字符串連接),列名是‘列名1 || 列名2 || 列名3’;
mysql> select s_no || s_name || s_age -> from student; +-------------------------+
| s_no || s_name || s_age |
+-------------------------+
| 1001張三23 |
| 1002李四19 |
| 1003馬五20 |
| 1004甲六17 |
| 1005乙七22 |
+-------------------------+
注意:
①如果不顯示結果,是因為sql_mode參數中沒有PIPES_AS_CONCAT,只要給sql_mode參數加入PIPES_AS_CONCAT,就可以實現像CONCAT一樣的功能;
②如果不給sql_mode參數加入PIPES_AS_CONCAT的話,|| 默認是or的意思,查詢結果是一列顯示是1。
5、SUBSTR(str,pos[,len]):從源字符串str中的指定位置pos開始取一個字串並返回
注意:
①len指定子串的長度,如果省略則一直取到字符串的末尾;len為負值表示從源字符串的尾部開始取起。
②函數SUBSTR()是函數SUBSTRING()的同義詞。
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):返回字符串的存儲長度
mysql> select length('text'),length('你好'); +----------------+------------------+
| length('text') | length('你好') |
+----------------+------------------+
| 4 | 6 |
+----------------+------------------+
注意:編碼方式不同字符串的存儲長度就不一樣(‘你好’:utf8是6,gbk是4)
7、CHAR_LENGTH(str):返回字符串中的字符個數
mysql> select char_length('text'),char_length('你好'); +---------------------+-----------------------+
| char_length('text') | char_length('你好') |
+---------------------+-----------------------+
| 4 | 2 |
+---------------------+-----------------------+
8、INSTR(str, substr):從源字符串str中返回子串substr第一次出現的位置
mysql> select instr('foobarbar','bar'); +--------------------------+
| instr('foobarbar','bar') |
+--------------------------+
| 4 |
+--------------------------+
9、LPAD(str, len, padstr):在源字符串的左邊填充給定的字符padstr到指定的長度len,返回填充后的字符串
mysql> select lpad('hi',5,'??'); +-------------------+
| lpad('hi',5,'??') |
+-------------------+
| ???hi |
+-------------------+
10、RPAD(str, len, padstr):在源字符串的右邊填充給定的字符padstr到指定的長度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):
從源字符串str中去掉兩端、前綴或后綴字符remstr並返回;
如果不指定remstr,則去掉str兩端的空格;
不指定BOTH、LEADING、TRAILING ,則默認為 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(大小寫敏感),找到后使用替代字符串to_str替換它。返回替換后的字符串
mysql> select replace('www.mysql.com','w','Ww'); +-----------------------------------+
| replace('www.mysql.com','w','Ww') |
+-----------------------------------+
| WwWwWw.mysql.com |
+-----------------------------------+
13、LTRIM(str),RTRIM(str):去掉字符串的左邊或右邊的空格(左對齊、右對齊)
mysql> SELECT ltrim(' barbar ') rs1, rtrim(' barbar ') rs2; +-----------+-----------+
| rs1 | rs2 |
+-----------+-----------+
| barbar | barbar |
+-----------+-----------+
14、REPEAT(str, count):將字符串str重復count次后返回
mysql> select repeat('MySQL',3); +-------------------+
| repeat('MySQL',3) |
+-------------------+
| MySQLMySQLMySQL |
+-------------------+
15、REVERSE(str):將字符串str反轉后返回
mysql> select reverse('abcdef'); +-------------------+
| reverse('abcdef') |
+-------------------+
| fedcba |
+-------------------+
16、CHAR(N,... [USING charset_name]):將每個參數N解釋為整數(字符的編碼),並返回每個整數對應的字符所構成的字符串(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 |
+-------------------------+----------------------+
默認情況下,函數返回二進制字符串,若想返回針對特定字符集的字符串,使用using選項
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‘#,###,###.##’格式化數字X
D指定小數位數
locale指定國家語言(默認的locale為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個空格構成的字符串
mysql> select space(3); +----------+
| space(3) |
+----------+
| |
+----------+
19、LEFT(str, len):返回最左邊的len長度的子串
mysql> select left('chinaitsoft',5); +-----------------------+
| left('chinaitsoft',5) |
+-----------------------+
| china |
+-----------------------+
20、RIGHT(str, len):返回最右邊的len長度的子串
mysql> select right('chinaitsoft',5); +------------------------+
| right('chinaitsoft',5) |
+------------------------+
| tsoft |
+------------------------+
21、STRCMP(expr1,expr2):如果兩個字符串是一樣的則返回0;如果第一個小於第二個則返回-1;否則返回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 |
+-------------------------+-------------------------+