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 程式師世界 >> 數據庫知識 >> MYSQL數據庫 >> MySQL綜合教程 >> MySQL筆記之運算符使用詳解

MySQL筆記之運算符使用詳解

編輯:MySQL綜合教程

Mysql可以通過運算符來對表中數據進行運算,比如通過出生日期求年齡等

運算符包括四類,分別是:算數運算符、比較運算符、邏輯運算符和位運算符


算數運算符
加、減、乘運算
復制代碼 代碼如下:
mysql> select a,a+5,a*2 from t1;
+------+------+------+
| a    | a+5  | a*2  |
+------+------+------+
|   24 |   29 |   48 |
+------+------+------+
 row in set (0.00 sec)

這裡的原值為24,後面也可以使用混合運算,只需要注意優先級即可


除法和取模運算
復制代碼 代碼如下:
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)

此處 / 和 div 代表整除,% 和 mod 代表取模

要注意的是,如果被除數為0,那麼計算結果是NULL


比較運算符
數值比較
復制代碼 代碼如下:
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)

這裡的1代表真,0代表假,需要說明的是<>和<=>

<>代表不等於,等同於!=

<=>代表等於,等同於=

此外,等於和不等於不僅可以比較數值,還能比較字符串


字符串比較
復制代碼 代碼如下:
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
復制代碼 代碼如下:
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)

這裡可以判斷是否為空,NULL也可以跟NULL比較


between and和not between and
復制代碼 代碼如下:
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可以判斷數值是否在某一區間內


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)
判斷操作數是否在某一集合內


like
復制代碼 代碼如下:
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可以用來匹配字符串,_代表單個字符,%代表多個字符


邏輯運算符
與運算
復制代碼 代碼如下:
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)

這裡&&和and意思一樣


或運算
復制代碼 代碼如下:
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)

這裡||和or的意思一樣


非運算
復制代碼 代碼如下:
mysql> select !1,!2,!null;
+----+----+-------+
| !1 | !2 | !null |
+----+----+-------+
|  0 |  0 |  NULL |
+----+----+-------+
 row in set (0.00 sec)

此外還有位運算,目前還沒用到,等用到的時候再補上

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