Mysql可以通过运算符来对表中数据进行运算，比如通过出生日期求年龄等 运算符包括四类，分别是：算数运算符、比较运算符、逻辑运算符和位运算符 算数运算符 加、减、乘运算 复制代码 代码如下: mysql> select a,a+5,a*2 from t1; +------+------+------+ | a | a+5 | a*2 | +------+------+------+ | 24 | 29 | 48 | +------+------+------+ row in set (0.00 sec) 这里的原值为24,后面也可以使用混合运算，只需要注意优先级即可 除法和取模运算 复制代码 代码如下: mysql> select a,a/3,a div 3,a%5,mod(a,5) from t1; +------+--------+---------+------+----------+ | a | a/3 | a div 3 | a%5 | mod(a,5) | +------+--------+---------+------+----------+ | 24 | 8.0000 | 8 | 4 | 4 | +------+--------+---------+------+----------+ row in set (0.00 sec) 此处 / 和 div 代表整除，% 和 mod 代表取模 要注意的是，如果被除数为0,那么计算结果是NULL 比较运算符 数值比较 复制代码 代码如下: mysql> select a,a=24,a<12,a>40,a>=24,a<=24,a!=24,a<>24,a<=>24 from t1; +------+------+------+------+-------+-------+-------+-------+--------+ | a | a=24 | a<12 | a>40 | a>=24 | a<=24 | a!=24 | a<>24 | a<=>24 | +------+------+------+------+-------+-------+-------+-------+--------+ | 24 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | +------+------+------+------+-------+-------+-------+-------+--------+ row in set (0.00 sec) 这里的1代表真，0代表假，需要说明的是<>和<=> <>代表不等于，等同于!= <=>代表等于，等同于= 此外，等于和不等于不仅可以比较数值，还能比较字符串 字符串比较 复制代码 代码如下: mysql> select a,a='24','ha'<>'ha','xa'='xa','b'!='b' from t1; +------+--------+------------+-----------+----------+ | a | a='24' | 'ha'<>'ha' | 'xa'='xa' | 'b'!='b' | +------+--------+------------+-----------+----------+ | 24 | 1 | 0 | 1 | 0 | +------+--------+------------+-----------+----------+ row in set (0.00 sec) is null 和is not null 复制代码 代码如下: mysql> select a,a is null, a is not null from t1; +------+-----------+---------------+ | a | a is null | a is not null | +------+-----------+---------------+ | 24 | 0 | 1 | +------+-----------+---------------+ row in set (0.00 sec) 这里可以判断是否为空，NULL也可以跟NULL比较 between and和not between and 复制代码 代码如下: mysql> select a,a between 15 and 30,a not between 15 and 30 from t1; +------+---------------------+-------------------------+ | a | a between 15 and 30 | a not between 15 and 30 | +------+---------------------+-------------------------+ | 24 | 1 | 0 | +------+---------------------+-------------------------+ row in set (0.00 sec) between and 和not between and可以判断数值是否在某一区间内 in mysql> select a,a in(1,2,23),a in(24,12,22) from t1; +------+--------------+----------------+ | a | a in(1,2,23) | a in(24,12,22) | +------+--------------+----------------+ | 24 | 0 | 1 | +------+--------------+----------------+ row in set (0.00 sec) 判断操作数是否在某一集合内 like 复制代码 代码如下: mysql> select s,s like 'beijing',s like 'b%g',s like 'bei____',s like '%jing' from t2; +---------+------------------+--------------+------------------+----------------+ | s | s like 'beijing' | s like 'b%g' | s like 'bei____' | s like '%jing' | +---------+------------------+--------------+------------------+----------------+ | beijing | 1 | 1 | 1 | 1 | +---------+------------------+--------------+------------------+----------------+ row in set (0.00 sec) ike可以用来匹配字符串，_代表单个字符，%代表多个字符 逻辑运算符 与运算 复制代码 代码如下: mysql> select 2&&2,2&&null,2 and 3,2 and 2; +------+---------+---------+---------+ | 2&&2 | 2&&null | 2 and 3 | 2 and 2 | +------+---------+---------+---------+ | 1 | NULL | 1 | 1 | +------+---------+---------+---------+ row in set (0.00 sec) 这里&&和and意思一样 或运算 复制代码 代码如下: mysql> select 2||2,2||null,2 or 3,2 or 0; +------+---------+--------+--------+ | 2||2 | 2||null | 2 or 3 | 2 or 0 | +------+---------+--------+--------+ | 1 | 1 | 1 | 1 | +------+---------+--------+--------+ row in set (0.00 sec) 这里||和or的意思一样 非运算 复制代码 代码如下:
