Mysql可以通過運(yùn)算符來對(duì)表中數(shù)據(jù)進(jìn)行運(yùn)算，比如通過出生日期求年齡等
運(yùn)算符包括四類，分別是：算數(shù)運(yùn)算符、比較運(yùn)算符、邏輯運(yùn)算符和位運(yùn)算符
算數(shù)運(yùn)算符
加、減、乘運(yùn)算
mysql> select a,a+5,a*2 from t1;
+------+------+------+
| a | a+5 | a*2 |
+------+------+------+
| 24 | 29 | 48 |
+------+------+------+
row in set (0.00 sec)
這里的原值為24,后面也可以使用混合運(yùn)算，只需要注意優(yōu)先級(jí)即可
除法和取模運(yùn)算
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)
此處 / 和 div 代表整除，% 和 mod 代表取模要注意的是，如果被除數(shù)為0,那么計(jì)算結(jié)果是NULL
比較運(yùn)算符
數(shù)值比較
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)
這里的1代表真，0代表假，需要說明的是<>和<=><>代表不等于，等同于!=
<=>代表等于，等同于=
此外，等于和不等于不僅可以比較數(shù)值，還能比較字符串
字符串比較
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
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)
這里可以判斷是否為空，NULL也可以跟NULL比較
between and和not between and
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可以判斷數(shù)值是否在某一區(qū)間內(nèi)
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)
判斷操作數(shù)是否在某一集合內(nèi)
like
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可以用來匹配字符串，_代表單個(gè)字符，%代表多個(gè)字符
邏輯運(yùn)算符
與運(yùn)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 |
+------+---------+---------+---------+
row in set (0.00 sec)
這里&&和and意思一樣
或運(yùn)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 |
+------+---------+--------+--------+
row in set (0.00 sec)
這里||和or的意思一樣
非運(yùn)算
mysql> select !1,!2,!null;
+----+----+-------+
| !1 | !2 | !null |
+----+----+-------+
| 0 | 0 | NULL |
+----+----+-------+
row in set (0.00 sec)
此外還有位運(yùn)算，目前還沒用到，等用到的時(shí)候再補(bǔ)上
