在mysql中 11div4_MySQL学习笔记11:运算符

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

mysql> select a,a+5,a*2 fromt1;+------+------+------+

| a | a+5 | a*2 |

+------+------+------+

| 24 | 29 | 48 |

+------+------+------+

1 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

mysql> select a,a/3,a div 3,a%5,mod(a,5) fromt1;+------+--------+---------+------+----------+

| a | a/3 | a div 3 | a%5 | mod(a,5) |

+------+--------+---------+------+----------+

| 24 | 8.0000 | 8 | 4 | 4 |

+------+--------+---------+------+----------+

1 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

mysql> select a,a=24,a<12,a>40,a>=24,a<=24,a!=24,a<>24,a<=>24 fromt1;+------+------+------+------+-------+-------+-------+-------+--------+

| 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 |

+------+------+------+------+-------+-------+-------+-------+--------+

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

mysql> select a,a='24','ha'<>'ha','xa'='xa','b'!='b' fromt1;+------+--------+------------+-----------+----------+

| a | a='24' | 'ha'<>'ha' | 'xa'='xa' | 'b'!='b' |

+------+--------+------------+-----------+----------+

| 24 | 1 | 0 | 1 | 0 |

+------+--------+------------+-----------+----------+

1 row in set (0.00 sec)

is null 和is not null

mysql> select a,a is null, a is not null fromt1;+------+-----------+---------------+

| a | a is null | a is not null |

+------+-----------+---------------+

| 24 | 0 | 1 |

+------+-----------+---------------+

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

mysql> select a,a between 15 and 30,a not between 15 and 30 fromt1;+------+---------------------+-------------------------+

| a | a between 15 and 30 | a not between 15 and 30 |

+------+---------------------+-------------------------+

| 24 | 1 | 0 |

+------+---------------------+-------------------------+

1 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) fromt1;+------+--------------+----------------+

| a | a in(1,2,23) | a in(24,12,22) |

+------+--------------+----------------+

| 24 | 0 | 1 |

+------+--------------+----------------+

1 row in set (0.00 sec)

判断操作数是否在某一集合内

like

mysql> select s,s like 'beijing',s like 'b%g',s like 'bei____',s like '%jing' fromt2;+---------+------------------+--------------+------------------+----------------+

| s | s like 'beijing' | s like 'b%g' | s like 'bei____' | s like '%jing' |

+---------+------------------+--------------+------------------+----------------+

| beijing | 1 | 1 | 1 | 1 |

+---------+------------------+--------------+------------------+----------------+

1 row in set (0.00 sec)

like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

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 |

+------+---------+---------+---------+

1 row in set (0.00 sec)

这里&&和and意思一样

或运算

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 |

+------+---------+--------+--------+

1 row in set (0.00 sec)

这里||和or的意思一样

非运算

mysql> select !1,!2,!null;+----+----+-------+

| !1 | !2 | !null |

+----+----+-------+

| 0 | 0 | NULL |

+----+----+-------+

1 row in set (0.00 sec)

此外还有位运算,目前还没用到,等用到的时候再补上

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