轉載自:http://www.cnblogs.com/xiangxiaodong/archive/2011/02/21/1959589.html
今天在論壇中看到一個關於mysql的問題,問題如下
good_id cat_id 12654 665,569 12655 601,4722
goods_id是商品id
cat_id是分類id
當我,怎麼根據這種分類ID查數據(一個商品有多個分類,而且用逗號隔開了)
我現在用的是like 這樣的話,輸入一個分類id是688,或者4722都能出來這個商品,但輸入一個722也出來這個商品了。
如果用like做的話,肯定會有問題的,我的開始的想法是,把cat_id裏面的字符串換成數組,這樣可以利用mysql裏面的in操作,這樣就不會出現查找722,而4722類別下的產品都跑出來了。我從網上找了半天,這方面的字符串操作函數,沒找到,不過我發現了find_in_set這個函數雖然不能,將字符串轉換成數組,但是也不會出現上面的情況。我發現自己有好多函數不知道,所以我從手冊中,以及網上收集了半天,做了一些例子。
一,測試準備
- 測試表
- CREATE TABLE `string_test` (
- `id` int(11) NOT NULL auto_increment COMMENT '用戶ID',
- `name` varchar(50) NOT NULL default '' COMMENT '名稱',
- `job` varchar(23) NOT NULL COMMENT '工作',
- `sex` tinyint(1) NOT NULL default '1' COMMENT '性別',
- `hobby` varchar(100) character set utf8 collate utf8_unicode_ci default NULL COMMENT '愛好',
- PRIMARY KEY (`id`)
- ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;
- 測試數據
- INSERT INTO `string_test` (`id`, `name`, `job`, `sex`, `hobby`) VALUES
- (1, 'tank', '農民工', 1, '軍棋,遊戲,fishing'),
- (2, 'zhang', 'DUCK', 0, 'fly,make firend'),
- (3, 'ying', 'no job', 1, 'flying,driving,testing'),
- (4, 'tankzhang', 'love your love', 1, 'i love you');
測試表 CREATE TABLE `string_test` ( `id` int(11) NOT NULL auto_increment COMMENT '用戶ID', `name` varchar(50) NOT NULL default '' COMMENT '名稱', `job` varchar(23) NOT NULL COMMENT '工作', `sex` tinyint(1) NOT NULL default '1' COMMENT '性別', `hobby` varchar(100) character set utf8 collate utf8_unicode_ci default NULL COMMENT '愛好', PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ; 測試數據 INSERT INTO `string_test` (`id`, `name`, `job`, `sex`, `hobby`) VALUES (1, 'tank', '農民工', 1, '軍棋,遊戲,fishing'), (2, 'zhang', 'DUCK', 0, 'fly,make firend'), (3, 'ying', 'no job', 1, 'flying,driving,testing'), (4, 'tankzhang', 'love your love', 1, 'i love you');
id | name | job | sex | hobby |
---|---|---|---|---|
1 | tank | 農民工 | 1 | 軍棋,遊戲,fishing |
2 | zhang | DUCK | 0 | fly,make firend |
3 | ying | no job | 1 | flying,driving,testing |
4 | tankzhang | love your love | 1 | i love you |
二,mysql字符串操作函數
1,UPPER和UCASE
返回字符串str,根據當前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改變成大寫。該函數對多字節是可靠的。
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,根據當前字符集映射(缺省是ISO-8859-1 Latin1)把所有的字符改變成小寫。該函數對多字節是可靠的。
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子串組成的表strlist之中,返回一個1到N的值。一個字符串表是被“,”分隔的子串組成的一個字符串。如果第一個參數是一個常數字符串並且第二個參數是一種類型爲SET的列,FIND_IN_SET()函數被優化而使用位運算!如果str不是在strlist裏面或如果 strlist是空字符串,返回0。如果任何一個參數是NULL,返回NULL。如果第一個參數包含一個“,”,該函數將工作不正常。看面是二種不同的效果,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, …清單的索引。如果str沒找到,返回0。FIELD()是ELT()反運算。
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小於1或大於參數個數,返回NULL。ELT()是FIELD()反運算。
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的所有出現由字符串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)
返回由重複countTimes次的字符串str組成的一個字符串。如果count <= 0,返回一個空字符串。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)
返回顛倒字符順序的字符串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個字符長得子串由字符串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)
從字符串str的起始位置pos返回一個子串。下面的sub2沒有值,因爲mysql數據庫的下標是從1開始的。
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)
返回從字符串str的第count個出現的分隔符delim之後的子串。如果count是正數,返回最後的分隔符到左邊(從左邊數) 的所有字符。如果count是負數,返回最後的分隔符到右邊的所有字符(從右邊數)。
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)
返回刪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)
返回刪除了其拖後空格字符的字符串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前綴或後綴被刪除了。如果沒有修飾符BOTH、LEADING或TRAILING給出,BOTH被假定。如果remstr沒被指定,空格被刪除。
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)
從字符串str返回一個len個字符的子串,從位置pos開始。使用FROM的變種形式是ANSI SQL92語法。
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填補直到str是len個字符長。
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填補直到str是len個字符長。
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個字符。
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個字符。
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,位置控制函數
POSITION(substr IN str)
返回子串substr在字符串str第一個出現的位置,如果substr不是在str裏面,返回0.
LOCATE(substr,str,pos)
返回子串substr在字符串str第一個出現的位置,從位置pos開始。如果substr不是在str裏面,返回0。
INSTR(str,substr)
返回子串substr在字符串str中的第一個出現的位置。這與有2個參數形式的LOCATE()相同,除了參數被顛倒。
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,得到字符串長度的函數
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,合併多個字符串,或者表中的多個字段
CONCAT(str1,str2,…)
返回來自於參數連結的字符串。如果任何參數是NULL,返回NULL。可以有超過2個的參數。一個數字參數被變換爲等價的字符串形式。
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,進制轉換
BIN(N)
返回二進制值N的一個字符串表示,在此N是一個長整數(BIGINT)數字,這等價於CONV(N,10,2)。如果N是NULL,返回NULL。
OCT(N)
返回八進制值N的一個字符串的表示,在此N是一個長整型數字,這等價於CONV(N,10,8)。如果N是NULL,返回NULL。
HEX(N)
返回十六進制值N一個字符串的表示,在此N是一個長整型(BIGINT)數字,這等價於CONV(N,10,16)。如果N是NULL,返回NULL。
ASCII(str)
返回字符串str的最左面字符的ASCII代碼值。如果str是空字符串,返回0。如果str是NULL,返回NULL。
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)
上面我只例舉了一部分對字符串進行操作的函數,並且是我覺得我們平時會用的,有可能會用到的一些函數。