今天在论坛中看到一个关于mysql的问题,问题如下 good_id cat_id 12654 665,569 12655 601,4722
goods_id是商品id
如果用like做的话,肯定会有问题的,我的开始的想法是,把cat_id里面的字符串换成数组,这样可以利用mysql里面的in操作,这样就不会出现查找722,而4722类别下的产品都跑出来了。我从网上找了半天,这方面的字符串操作函数,没找到,不过我发现了find_in_set这个函数虽然不能,将字符串转换成数组,但是也不会出现上面的情况。我发现自己有好多函数不知道,所以我从手册中,以及网上收集了半天,做了一些例子。 一,测试准备
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二,mysql字符串操作函数 1,UPPER和UCASE 返回字符串str,根据当前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改变成大写。该函数对多字节是可靠的。 mysql> select name,UPPER(name) from string_test where name='tank'; +------+-------------+ | name | UPPER(name) | +------+-------------+ | tank | TANK | +------+-------------+ 1 row in set (0.00 sec) 2,LOWER和LCASE 返回字符串str,根据当前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改变成小写。该函数对多字节是可靠的。 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) 如果字符串str在由N子串组成的表strlist之中,返回一个1到N的值。一个字符串表是被“,”分隔的子串组成的一个字符串。如果第一个参数是一个常数字符串并且第二个参数是一种类型为SET的列,FIND_IN_SET()函数被优化而使用位运算!如果str不是在strlist里面或如果strlist是空字符串,返回0。如果任何一个参数是NULL,返回NULL。如果第一个参数包含一个“,”,该函数将工作不正常。看面是二种不同的效果,可以看一下 mysql> SELECT id,name FROM string_test WHERE find_in_set('fly',hobby); +----+-------+ | id | name | +----+-------+ | 2 | zhang | +----+-------+ 1 row in set (0.00 sec) mysql> SELECT id,name FROM string_test WHERE hobby like 'fly%'; +----+-------+ | id | name | +----+-------+ | 2 | zhang | | 3 | ying | +----+-------+ 2 rows in set (0.00 sec) 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> SELECT id, 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 FROM s tring_test WHERE id =4; +----+--------+------+-----------+---------+ | id | sub1 | sub2 | sub3 | sub4 | +----+--------+------+-----------+---------+ | 4 | i love | | love you | ove you | +----+--------+------+-----------+---------+ 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" from jo b) as test2,TRIM(TRAILING "love" from job) as test3 FROM string_test WHERE id = 4 -> ; +----+------------+--------+------------+ | id | test1 | test2 | test3 | +----+------------+--------+------------+ | 4 | your love | your | love your | +----+------------+--------+------------+ 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 ) AS sub1, mid( hobby -> FROM 0 -> FOR 8 ) AS sub2, mid( hobby, 2 ) AS sub3, mid( hobby -> FROM 4 ) AS sub4 -> FROM string_test -> WHERE id =4 ; +----+--------+------+-----------+---------+ | id | sub1 | sub2 | sub3 | sub4 | +----+--------+------+-----------+---------+ | 4 | i love | | love you | ove you | +----+--------+------+-----------+---------+ 1 row in set (0.00 sec) mysql> 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)
LOCATE(substr,str,pos)
INSTR(str,substr) mysql> SELECT id,INSTR(job,"you") as instr,LOCATE('love',job,3) as locate,POSITI ON('love' in job) as position FROM string_test WHERE id = 4; +----+-------+--------+----------+ | id | instr | locate | position | +----+-------+--------+----------+ | 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) as three,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)
OCT(N)
HEX(N)
ASCII(str) 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。 (责任编辑:IT) |