mysql 運(yùn)算符

mysql 的運(yùn)算符包括算術(shù)運(yùn)算符、比較運(yùn)算符、邏輯運(yùn)算符、位運(yùn)算符等。運(yùn)算符之間存在著優(yōu)先級(jí)。

如果我們無(wú)法記住運(yùn)算符的優(yōu)先級(jí)，可以直接通過(guò)小括號(hào)來(lái)改變優(yōu)先級(jí)。

mysql 主要有以下幾種運(yùn)算符：

• 算術(shù)運(yùn)算符
• 比較運(yùn)算符
• 邏輯運(yùn)算符
• 位運(yùn)算符

1. 算術(shù)運(yùn)算符

mysql 支持的算術(shù)運(yùn)算符包括:

在除法運(yùn)算和模運(yùn)算中，如果除數(shù)為0，將是非法除數(shù)，返回結(jié)果為null。

1、加

mysql> select 1+2;
+-----+
| 1+2 |
+-----+
|   3 |
+-----+

2、減

mysql> select 1-2;
+-----+
| 1-2 |
+-----+
|  -1 |
+-----+

3、乘

mysql> select 2*3;
+-----+
| 2*3 |
+-----+
|   6 |
+-----+

4、除

mysql> select 2/3;
+--------+
| 2/3    |
+--------+
| 0.6667 |
+--------+

5、商

mysql> select 10 div 4;
+----------+
| 10 div 4 |
+----------+
|        2 |
+----------+

6、取余

mysql> select 10 mod 4;
+----------+
| 10 mod 4 |
+----------+
|        2 |
+----------+

2. 比較運(yùn)算符

select 語(yǔ)句中的條件語(yǔ)句經(jīng)常要使用比較運(yùn)算符。通過(guò)這些比較運(yùn)算符，可以判斷表中的哪些記錄是符合條件的。比較結(jié)果為真，則返回 1，為假則返回 0，比較結(jié)果不確定則返回 null。

1、等于

mysql> select 2=3;
+-----+
| 2=3 |
+-----+
|   0 |
+-----+


mysql> select null = null;
+-------------+
| null = null |
+-------------+
|        null |
+-------------+

2、不等于

mysql> select 2<>3;
+------+
| 2<>3 |
+------+
|    1 |
+------+

3、安全等于

與 = 的區(qū)別在于當(dāng)兩個(gè)操作碼均為 null 時(shí)，其所得值為 1 而不為 null，而當(dāng)一個(gè)操作碼為 null 時(shí)，其所得值為 0而不為 null。

mysql> select 2<=>3;
+-------+
| 2<=>3 |
+-------+
|     0 |
+-------+


mysql> select null=null;
+-----------+
| null=null |
+-----------+
|      null |
+-----------+

        
mysql> select null<=>null;
+-------------+
| null<=>null |
+-------------+
|           1 |
+-------------+

4、小于

mysql> select 2<3;
+-----+
| 2<3 |
+-----+
|   1 |
+-----+

5、小于等于

mysql> select 2<=3;
+------+
| 2<=3 |
+------+
|    1 |
+------+

6、大于

mysql> select 2>3;
+-----+
| 2>3 |
+-----+
|   0 |
+-----+

7、大于等于

mysql> select 2>=3;
+------+
| 2>=3 |
+------+
|    0 |
+------+

8、between

mysql> select 5 between 1 and 10;
+--------------------+
| 5 between 1 and 10 |
+--------------------+
|                  1 |
+--------------------+

9、in

mysql> select 5 in (1,2,3,4,5);
+------------------+
| 5 in (1,2,3,4,5) |
+------------------+
|                1 |
+------------------+

10、not in

mysql> select 5 not in (1,2,3,4,5);
+----------------------+
| 5 not in (1,2,3,4,5) |
+----------------------+
|                    0 |
+----------------------+

11、is null

mysql> select null is null;
+--------------+
| null is null |
+--------------+
|            1 |
+--------------+

mysql> select 'a' is null;
+-------------+
| 'a' is null |
+-------------+
|           0 |
+-------------+

12、is not null

mysql> select null is not null;
+------------------+
| null is not null |
+------------------+
|                0 |
+------------------+

        
mysql> select 'a' is not null;
+-----------------+
| 'a' is not null |
+-----------------+
|               1 |
+-----------------+

13、like

mysql> select '12345' like '12%';
+--------------------+
| '12345' like '12%' |
+--------------------+
|                  1 |
+--------------------+

mysql> select '12345' like '12_';
+--------------------+
| '12345' like '12_' |
+--------------------+
|                  0 |
+--------------------+

14、regexp

mysql> select 'beijing' regexp 'jing';
+-------------------------+
| 'beijing' regexp 'jing' |
+-------------------------+
|                       1 |
+-------------------------+

mysql> select 'beijing' regexp 'xi';
+-----------------------+
| 'beijing' regexp 'xi' |
+-----------------------+
|                     0 |
+-----------------------+

3. 邏輯運(yùn)算符

邏輯運(yùn)算符用來(lái)判斷表達(dá)式的真假。如果表達(dá)式是真，結(jié)果返回 1。如果表達(dá)式是假，結(jié)果返回 0。

1、與

mysql> select 2 and 0;
+---------+
| 2 and 0 |
+---------+
|       0 |
+---------+

        
mysql> select 2 and 1;   
+---------+     
| 2 and 1 |      
+---------+      
|       1 |      
+---------+

2、或

mysql> select 2 or 0;
+--------+
| 2 or 0 |
+--------+
|      1 |
+--------+

mysql> select 2 or 1;
+--------+
| 2 or 1 |
+--------+
|      1 |
+--------+

mysql> select 0 or 0;
+--------+
| 0 or 0 |
+--------+
|      0 |
+--------+

mysql> select 1 || 0;
+--------+
| 1 || 0 |
+--------+
|      1 |
+--------+

3、非

mysql> select not 1;
+-------+
| not 1 |
+-------+
|     0 |
+-------+

mysql> select !0;
+----+
| !0 |
+----+
|  1 |
+----+

4、異或

mysql> select 1 xor 1;
+---------+
| 1 xor 1 |
+---------+
|       0 |
+---------+

mysql> select 0 xor 0;
+---------+
| 0 xor 0 |
+---------+
|       0 |
+---------+

mysql> select 1 xor 0;
+---------+
| 1 xor 0 |
+---------+
|       1 |
+---------+

mysql> select null or 1;
+-----------+
| null or 1 |
+-----------+
|         1 |
+-----------+

mysql> select 1 ^ 0;
+-------+
| 1 ^ 0 |
+-------+
|     1 |
+-------+

4. 位運(yùn)算符

位運(yùn)算符是在二進(jìn)制數(shù)上進(jìn)行計(jì)算的運(yùn)算符。位運(yùn)算會(huì)先將操作數(shù)變成二進(jìn)制數(shù)，進(jìn)行位運(yùn)算。然后再將計(jì)算結(jié)果從二進(jìn)制數(shù)變回十進(jìn)制數(shù)。

1、按位與

mysql> select 3&5;
+-----+
| 3&5 |
+-----+
|   1 |
+-----+

2、按位或

mysql> select 3|5;
+-----+
| 3|5 |
+-----+
|   7 |
+-----+

3、按位異或

mysql> select 3^5;
+-----+
| 3^5 |
+-----+
|   6 |
+-----+

4、按位取反

mysql> select ~18446744073709551612;
+-----------------------+
| ~18446744073709551612 |
+-----------------------+
|                     3 |
+-----------------------+

5、按位右移

mysql> select 3>>1;
+------+
| 3>>1 |
+------+
|    1 |
+------+

6、按位左移

mysql> select 3<<1;
+------+
| 3<<1 |
+------+
|    6 |
+------+

5. 運(yùn)算符優(yōu)先級(jí)

最低優(yōu)先級(jí)為： :=。

最高優(yōu)先級(jí)為： !、binary、 collate。