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1¡¢LOWER(column|str)£º½«×Ö·û´®²ÎÊýֵת»»ÎªÈ«Ð¡Ð´×Öĸºó·µ»Ø
mysql> select lower('SQL Course');+---------------------+ | lower('SQL Course') | +---------------------+ | sql course | +---------------------+
2¡¢UPPER(column|str)£º½«×Ö·û´®²ÎÊýֵת»»ÎªÈ«´óд×Öĸºó·µ»Ø
mysql> select upper('Use MYsql');+--------------------+ | upper('Use MYsql') | +--------------------+ | USE MYSQL | +--------------------+
3¡¢CONCAT(column|str1, column|str2,...)£º½«¶à¸ö×Ö·û´®²ÎÊýÊ×βÏàÁ¬ºó·µ»Ø
mysql> select concat('My','S','QL');+-----------------------+ | concat('My','S','QL') | +-----------------------+ | MySQL | +-----------------------+
¼ÙÈçÓÐÈκβÎÊýΪnull£¬Ôòº¯Êý·µ»Ønull
mysql> select concat('My',null,'QL');+------------------------+ | concat('My',null,'QL') | +------------------------+ | NULL | +------------------------+
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mysql> select concat(14.3,'mysql');+----------------------+ | concat(14.3,'mysql') | +----------------------+ | 14.3mysql | +----------------------+
4¡¢CONCAT_WS(separator,str1,str2,...)£º½«¶à¸ö×Ö·û´®²ÎÊýÒÔ¸ø¶¨µÄ·Ö¸ô·ûseparatorÊ×βÏàÁ¬ºó·µ»Ø
mysql> select concat_ws(';','First name','Second name','Last name');+-------------------------------------------------------+ | concat_ws(';','First name','Second name','Last name') | +-------------------------------------------------------+ | First name;Second name;Last name | +-------------------------------------------------------+
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5¡¢SUBSTR(str,pos[,len])£º´ÓÔ´×Ö·û´®strÖеÄÖ¸¶¨Î»ÖÃpos¿ª¶ËÈ¡Ò»¸ö×Ö´®²¢·µ»Ø
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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)£º·µ»Ø×Ö·û´®µÄ´¢±¸³¤¶È
mysql> select length('text'),length('ÄãºÃ');+----------------+------------------+ | length('text') | length('ÄãºÃ') | +----------------+------------------+ | 4 | 6 | +----------------+------------------+
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7¡¢CHAR_LENGTH(str)£º·µ»Ø×Ö·û´®ÖеÄ×Ö·û¸öÊý
mysql> select char_length('text'),char_length('ÄãºÃ');+---------------------+-----------------------+ | char_length('text') | char_length('ÄãºÃ') | +---------------------+-----------------------+ | 4 | 2 | +---------------------+-----------------------+
8¡¢INSTR(str, substr)£º´ÓÔ´×Ö·û´®strÖзµ»Ø×Ó´®substrµÚÒ»´ÎÏÔÏÖµÄλÖÃ
mysql> select instr('foobarbar','bar');+--------------------------+ | instr('foobarbar','bar') | +--------------------------+ | 4 | +--------------------------+
9¡¢LPAD(str, len, padstr)£ºÔÚÔ´×Ö·û´®µÄ×ó±ßÌî³ä¸ø¶¨µÄ×Ö·ûpadstrµ½Ö¸¶¨µÄ³¤¶Èlen£¬·µ»ØÌî³äºóµÄ×Ö·û´®
mysql> select lpad('hi',5,'??');+-------------------+ | lpad('hi',5,'??') | +-------------------+ | ???hi | +-------------------+
10¡¢RPAD(str, len, padstr)£ºÔÚÔ´×Ö·û´®µÄÓÒ²àÌî³ä¸ø¶¨µÄ×Ö·ûpadstrµ½Ö¸¶¨µÄ³¤¶Èlen£¬·µ»ØÌî³äºóµÄ×Ö·û´®
mysql> select rpad('hi',6,'??');+-------------------+| rpad('hi',6,'??') |+-------------------+| hi???? |+-------------------+
11¡¢TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str), TRIM([remstr FROM] str)£º
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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)£ºÔÚÔ´×Ö·û´®strÖвéÑ°ËùÓеÄ×Ó´®form_str£¨´óСдÃôÈñ£©£¬Ñ°µ½ºóʹÓÃÌæ»»×Ö·û´®to_str¸ü»»Ëü¡£·µ»Ø¸ü»»ºóµÄ×Ö·û´®
mysql> select replace('www.mysql.com','w','Ww');+-----------------------------------+ | replace('www.mysql.com','w','Ww') | +-----------------------------------+ | WwWwWw.mysql.com | +-----------------------------------+
13¡¢LTRIM(str)£¬RTRIM(str)£ºÈ¥³ý×Ö·û´®µÄ×ó±ß»òÓÒ²àµÄ¿Õ¸ñ(×ó¶ÔÆë¡¢ÓÒ¶ÔÆë)
mysql> SELECT ltrim(' barbar ') rs1, rtrim(' barbar ') rs2;+-----------+-----------+ | rs1 | rs2 | +-----------+-----------+ | barbar | barbar | +-----------+-----------+
14¡¢REPEAT(str, count)£º½«×Ö·û´®str·´¸´count´Îºó·µ»Ø
mysql> select repeat('MySQL',3);+-------------------+ | repeat('MySQL',3) | +-------------------+ | MySQLMySQLMySQL | +-------------------+
15¡¢REVERSE(str)£º½«×Ö·û´®str·´×ªºó·µ»Ø
mysql> select reverse('abcdef');+-------------------+ | reverse('abcdef') | +-------------------+ | fedcba | +-------------------+
16¡¢CHAR(N,... [USING charset_name])£º½«Ã¿¸ö²ÎÊýN˵Ã÷ΪÕûÊý£¨×Ö·ûµÄ±àÂ룩£¬²¢·µ»Øÿ¸öÕûÊý¶ÔÓ¦µÄ×Ö·ûËù¹¹³ÉµÄ×Ö·û´®(NULLÖµ±»ºöÂÔ)¡£
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 | +-------------------------+----------------------+
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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])£ºÒÔ¸ñ¾Ö¡®#,###,###.##¡¯¸ñ¾Ö»¯Êý×ÖX
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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)£º·µ»ØÓÉN¸ö¿Õ¸ñ¹¹³ÉµÄ×Ö·û´®
mysql> select space(3);+----------+ | space(3) | +----------+ | | +----------+
19¡¢LEFT(str, len)£º·µ»Ø×î×ó±ßµÄlen³¤¶ÈµÄ×Ó´®
mysql> select left('chinaitsoft',5);+-----------------------+ | left('chinaitsoft',5) | +-----------------------+ | china | +-----------------------+
20¡¢RIGHT(str, len)£º·µ»Ø×îÓÒ²àµÄlen³¤¶ÈµÄ×Ó´®
mysql> select right('chinaitsoft',5);+------------------------+ | right('chinaitsoft',5) | +------------------------+ | tsoft | +------------------------+
21¡¢STRCMP(expr1,expr2)£º¼ÙÈçÁ½¸ö×Ö·û´®ÊÇÒ»ÑùµÄÔò·µ»Ø0£»¼ÙÈçµÚÒ»¸öСÓÚµÚ¶þ¸öÔò·µ»Ø-1£»²»È»·µ»Ø1
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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