MySQL 教程
MySQL 運(yùn)算符
本章節(jié)我們主要介紹 MySQL 的運(yùn)算符及運(yùn)算符的優(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
算術(shù)運(yùn)算符
MySQL 支持的算術(shù)運(yùn)算符包括:
| 運(yùn)算符 | 作用 |
|---|---|
| + | 加法 |
| - | 減法 |
| * | 乘法 |
| / 或 DIV | 除法 |
| % 或 MOD | 取余 |
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 | +----------+
比較運(yùn)算符
SELECT 語句中的條件語句經(jīng)常要使用比較運(yùn)算符。通過這些比較運(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。
| 符號(hào) | 描述 | 備注 |
|---|---|---|
| = | 等于 | |
| <>, != | 不等于 | |
| > | 大于 | |
| < | 小于 | |
| <= | 小于等于 | |
| >= | 大于等于 | |
| BETWEEN | 在兩值之間 | >=min&&<=max |
| NOT BETWEEN | 不在兩值之間 | |
| IN | 在集合中 | |
| NOT IN | 不在集合中 | |
| <=> | 嚴(yán)格比較兩個(gè)NULL值是否相等 | 兩個(gè)操作碼均為NULL時(shí)，其所得值為1；而當(dāng)一個(gè)操作碼為NULL時(shí)，其所得值為0 |
| LIKE | 模糊匹配 | |
| REGEXP 或 RLIKE | 正則式匹配 | |
| IS NULL | 為空 | |
| IS NOT NULL | 不為空 |
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 | +-----------------------+
邏輯運(yùn)算符
邏輯運(yùn)算符用來判斷表達(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。
| 運(yùn)算符號(hào) | 作用 |
|---|---|
| NOT 或 ! | 邏輯非 |
| AND | 邏輯與 |
| OR | 邏輯或 |
| XOR | 邏輯異或 |
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 | +-------+
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)。
| 運(yùn)算符號(hào) | 作用 |
|---|---|
| & | 按位與 |
| | | 按位或 |
| ^ | 按位異或 |
| ! | 取反 |
| << | 左移 |
| >> | 右移 |
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 | +------+
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。