介绍
正则表达式用来描述或者匹配符合规则的字符串。它的用法和like比较相似,但是它又比like更强大,能够实现一些很特殊的规则匹配;正则表达式需要使用REGEXP命令,匹配上返回”1″匹配不上返回”0″,默认不加条件REGEXP相当于like ‘%%’。在前面加上NOT相当于NOT LIKE。
命令 | 说明 |
^ | 在字符的开启处进行匹配 |
$ | 在字符的末尾处进行匹配 |
. | 匹配任何字符(包括回车和新行) |
[….] | 匹配括号内的任意单个字符 |
[m-n] | 匹配m到n之间的任意单个字符,例如[0-9],[a-z],[A-Z] |
[^..] | 不能匹配括号内的任意单个字符 |
a* | 匹配0个或多个a,包括空 |
a+ | 匹配一个或多个a,不包括空 |
a? | 匹配一个或0个a |
a1| a2 | 匹配a1或a2 |
a{m} | 匹配m个a |
a{m,} | 匹配m个或者更多个a |
a{m,n} | 匹配m到n个a |
a{,n} | 匹配0到n个a |
(….) | 将模式元素组成单一元素,例如(do)*意思是匹配0个多或多个do |
^
在字符串开始处进行匹配
mysql> SELECT 'abc' REGEXP '^a'; +-------------------+ | 'abc' REGEXP '^a' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec)
$
在字符串末尾开始匹配
mysql> SELECT 'abc' REGEXP 'a$'; +-------------------+ | 'abc' REGEXP 'a$' | +-------------------+ | 0 | +-------------------+ 1 row in set (0.01 sec) mysql> SELECT 'abc' REGEXP 'c$'; +-------------------+ | 'abc' REGEXP 'c$' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec)
.
匹配任意字符
mysql> SELECT 'abc' REGEXP '.a'; +-------------------+ | 'abc' REGEXP '.a' | +-------------------+ | 0 | +-------------------+ 1 row in set (0.00 sec) mysql> SELECT 'abc' REGEXP '.b'; +-------------------+ | 'abc' REGEXP '.b' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec) mysql> SELECT 'abc' REGEXP '.c'; +-------------------+ | 'abc' REGEXP '.c' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec) mysql> SELECT 'abc' REGEXP 'a.'; +-------------------+ | 'abc' REGEXP 'a.' | +-------------------+ | 1 | +-------------------+ 1 row in set (0.00 sec)
[…]
匹配括号内的任意单个字符
mysql> SELECT 'abc' REGEXP '[xyz]'; +----------------------+ | 'abc' REGEXP '[xyz]' | +----------------------+ | 0 | +----------------------+ 1 row in set (0.00 sec) mysql> SELECT 'abc' REGEXP '[xaz]'; +----------------------+ | 'abc' REGEXP '[xaz]' | +----------------------+ | 1 | +----------------------+ 1 row in set (0.00 sec)
[^…]:注意^符合只有在[]内才是取反的意思,在别的地方都是表示开始处匹配
匹配不出括号没的任意个字符,注意:REGEXP 前的匹配字符作为一个整体
mysql> SELECT 'a' REGEXP '[^abc]'; +---------------------+ | 'a' REGEXP '[^abc]' | +---------------------+ | 0 | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT 'x' REGEXP '[^abc]'; +---------------------+ | 'x' REGEXP '[^abc]' | +---------------------+ | 1 | +---------------------+ 1 row in set (0.00 sec)
mysql> SELECT 'abc' REGEXP '[^a]'; +---------------------+ | 'abc' REGEXP '[^a]' | +---------------------+ | 1 | +---------------------+ 1 row in set (0.00 sec)
‘abc’作为一个整体,所以它匹配不了a
a*
匹配0个或多个a,包括空字符串。
mysql> SELECT ‘stab’ REGEXP ‘.ta*b’;
+———————–+
| ‘stab’ REGEXP ‘.ta*b’ |
+———————–+
| 1 |
+———————–+
1 row in set (0.00 sec)
mysql> SELECT ‘stb’ REGEXP ‘.ta*b’;
+———————-+
| ‘stb’ REGEXP ‘.ta*b’ |
+———————-+
| 1 |
+———————-+
1 row in set (0.00 sec)
mysql> SELECT '' REGEXP 'a*'; +----------------+ | '' REGEXP 'a*' | +----------------+ | 1 | +----------------+ 1 row in set (0.00 sec)
a+
匹配1个或者多个a,但是不包括空字符
mysql> SELECT 'stab' REGEXP '.ta+b'; +-----------------------+ | 'stab' REGEXP '.ta+b' | +-----------------------+ | 1 | +-----------------------+ 1 row in set (0.00 sec) mysql> SELECT 'stb' REGEXP '.ta+b'; +----------------------+ | 'stb' REGEXP '.ta+b' | +----------------------+ | 0 | +----------------------+ 1 row in set (0.00 sec)
a?
匹配0个或者1个a
mysql> SELECT 'stb' REGEXP '.ta?b'; +----------------------+ | 'stb' REGEXP '.ta?b' | +----------------------+ | 1 | +----------------------+ 1 row in set (0.00 sec) mysql> SELECT 'stab' REGEXP '.ta?b'; +-----------------------+ | 'stab' REGEXP '.ta?b' | +-----------------------+ | 1 | +-----------------------+ 1 row in set (0.00 sec) mysql> SELECT 'staab' REGEXP '.ta?b'; +------------------------+ | 'staab' REGEXP '.ta?b' | +------------------------+ | 0 | +------------------------+ 1 row in set (0.00 sec)
a1|a2
匹配a1或者a2,
mysql> SELECT 'a' REGEXP 'a|b'; +------------------+ | 'a' REGEXP 'a|b' | +------------------+ | 1 | +------------------+ 1 row in set (0.00 sec) mysql> SELECT 'b' REGEXP 'a|b'; +------------------+ | 'b' REGEXP 'a|b' | +------------------+ | 1 | +------------------+ 1 row in set (0.00 sec) mysql> SELECT 'b' REGEXP '^(a|b)'; +---------------------+ | 'b' REGEXP '^(a|b)' | +---------------------+ | 1 | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT 'a' REGEXP '^(a|b)'; +---------------------+ | 'a' REGEXP '^(a|b)' | +---------------------+ | 1 | +---------------------+ 1 row in set (0.00 sec) mysql> SELECT 'c' REGEXP '^(a|b)'; +---------------------+ | 'c' REGEXP '^(a|b)' | +---------------------+ | 0 | +---------------------+ 1 row in set (0.00 sec)
注意:^符合只有在[]内才是取反的意思,在别的地方都是表示开始处匹配
a{m}
匹配m个a
mysql> SELECT 'auuuuc' REGEXP 'au{4}c'; +--------------------------+ | 'auuuuc' REGEXP 'au{4}c' | +--------------------------+ | 1 | +--------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'auuuuc' REGEXP 'au{3}c'; +--------------------------+ | 'auuuuc' REGEXP 'au{3}c' | +--------------------------+ | 0 | +--------------------------+ 1 row in set (0.00 sec)
a{m,}
匹配m个或者更多个a
mysql> SELECT 'auuuuc' REGEXP 'au{3,}c'; +---------------------------+ | 'auuuuc' REGEXP 'au{3,}c' | +---------------------------+ | 1 | +---------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'auuuuc' REGEXP 'au{4,}c'; +---------------------------+ | 'auuuuc' REGEXP 'au{4,}c' | +---------------------------+ | 1 | +---------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'auuuuc' REGEXP 'au{5,}c'; +---------------------------+ | 'auuuuc' REGEXP 'au{5,}c' | +---------------------------+ | 0 | +---------------------------+ 1 row in set (0.00 sec)
a{m,n}
匹配m到n个a,包含m和n
mysql> SELECT 'auuuuc' REGEXP 'au{3,5}c'; +----------------------------+ | 'auuuuc' REGEXP 'au{3,5}c' | +----------------------------+ | 1 | +----------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'auuuuc' REGEXP 'au{4,5}c'; +----------------------------+ | 'auuuuc' REGEXP 'au{4,5}c' | +----------------------------+ | 1 | +----------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'auuuuc' REGEXP 'au{5,10}c'; +-----------------------------+ | 'auuuuc' REGEXP 'au{5,10}c' | +-----------------------------+ | 0 | +-----------------------------+ 1 row in set (0.00 sec)
a{,n}
这个暂时还没有测出来,意思应该不是匹配0到n个a,如果是表达0到n个a也可以用{0,n}代替
(abc)
将abc作为一个序列匹配,不用括号括起来都是用单个字符去匹配,如果要把多个字符作为一个整体去匹配就需要用到括号,所以括号适合上面的所有情况。
mysql> SELECT 'xababy' REGEXP 'x(abab)y'; +----------------------------+ | 'xababy' REGEXP 'x(abab)y' | +----------------------------+ | 1 | +----------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'xababy' REGEXP 'x(ab)*y'; +---------------------------+ | 'xababy' REGEXP 'x(ab)*y' | +---------------------------+ | 1 | +---------------------------+ 1 row in set (0.00 sec) mysql> SELECT 'xababy' REGEXP 'x(ab){1,2}y'; +-------------------------------+ | 'xababy' REGEXP 'x(ab){1,2}y' | +-------------------------------+ | 1 | +-------------------------------+ 1 row in set (0.00 sec)
总结
特别要注意最后的()的命令,如果不使用()那么所有的都是指单个字符去做匹配,如果需要使用多个字符作为一个整体去匹配就需要将多个字符使用()给括起来
1.使用REGEXP和NOT REGEXP操作符(类似LIKE和NOT LIKE);
2.REGEXP默认也是不区分大小写,可以使用BINARY关键词强制区分大小写; WHERE NAME REGEXP BINARY ‘^[A-Z]’;
3.REGEXP默认是部分匹配原则,即有一个匹配上则返回真。例如:SELECT ‘Abc’ REGEXP BINARY ‘[A-Z]’;
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