操作符

每个操作符都是一个保留字，主要用于在 SQL 语句的 WHERE 子句中执行各种操作，例如比较和算术运算等。

操作符在 SQL 语句中指定了条件，并可以将同一语句中的不同条件连接起来。

算术运算符
比较运算符
逻辑运算符
用于否定条件的运算符

SQL 算术运算符

这里一些有关 SQL 算术运算符如何使用的简单示例：

    SQL> select 10+ 20;
    +--------+
    | 10+ 20 |
    +--------+
    |     30 |
    +--------+
    1 row in set (0.00 sec)

    SQL> select 10 * 20;
    +---------+
    | 10 * 20 |
    +---------+
    |     200 |
    +---------+
    1 row in set (0.00 sec)

    SQL> select 10 / 5;
    +--------+
    | 10 / 5 |
    +--------+
    | 2.0000 |
    +--------+
    1 row in set (0.03 sec)

    SQL> select 12 %  5;
    +---------+
    | 12 %  5 |
    +---------+
    |       2 |
    +---------+
    1 row in set (0.00 sec)

假设变量 a 的值为 10，变量 b 的值为 20，那么：

操作符	描述	示例
+	相加：将符号两边的数值加起来。	a + b 得 30
-	相减：从最边的操作数中减去右边的操作数。	a - b 得 -10
*	相乘：将两边的操作数相乘。	a * b 得 200
/	相除：用右边的操作数除以左边的操作数。	b / a 得 2
%	取余：用右边的操作数除以左边的操作数，并返回余数。	b % a 得 0

SQL 比较运算符

考虑 CUSTOMERS 表，表中的记录如下所示：

    SQL> SELECT * FROM CUSTOMERS;
    +----+----------+-----+-----------+----------+
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
    |  3 | kaushik  |  23 | Kota      |  2000.00 |
    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  6 | Komal    |  22 | MP        |  4500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+
    7 rows in set (0.00 sec)

下面是一些关于如何使用 SQL 比较运算符的简单示例：

    SQL> SELECT * FROM CUSTOMERS WHERE SALARY > 5000;
    +----+----------+-----+---------+----------+
    | ID | NAME     | AGE | ADDRESS | SALARY   |
    +----+----------+-----+---------+----------+
    |  4 | Chaitali |  25 | Mumbai  |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal  |  8500.00 |
    |  7 | Muffy    |  24 | Indore  | 10000.00 |
    +----+----------+-----+---------+----------+
    3 rows in set (0.00 sec)

    SQL>  SELECT * FROM CUSTOMERS WHERE SALARY = 2000;
    +----+---------+-----+-----------+---------+
    | ID | NAME    | AGE | ADDRESS   | SALARY  |
    +----+---------+-----+-----------+---------+
    |  1 | Ramesh  |  32 | Ahmedabad | 2000.00 |
    |  3 | kaushik |  23 | Kota      | 2000.00 |
    +----+---------+-----+-----------+---------+
    2 rows in set (0.00 sec)

    SQL>  SELECT * FROM CUSTOMERS WHERE SALARY != 2000;
    +----+----------+-----+---------+----------+
    | ID | NAME     | AGE | ADDRESS | SALARY   |
    +----+----------+-----+---------+----------+
    |  2 | Khilan   |  25 | Delhi   |  1500.00 |
    |  4 | Chaitali |  25 | Mumbai  |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal  |  8500.00 |
    |  6 | Komal    |  22 | MP      |  4500.00 |
    |  7 | Muffy    |  24 | Indore  | 10000.00 |
    +----+----------+-----+---------+----------+
    5 rows in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE SALARY <> 2000;
    +----+----------+-----+---------+----------+
    | ID | NAME     | AGE | ADDRESS | SALARY   |
    +----+----------+-----+---------+----------+
    |  2 | Khilan   |  25 | Delhi   |  1500.00 |
    |  4 | Chaitali |  25 | Mumbai  |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal  |  8500.00 |
    |  6 | Komal    |  22 | MP      |  4500.00 |
    |  7 | Muffy    |  24 | Indore  | 10000.00 |
    +----+----------+-----+---------+----------+
    5 rows in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE SALARY >= 6500;
    +----+----------+-----+---------+----------+
    | ID | NAME     | AGE | ADDRESS | SALARY   |
    +----+----------+-----+---------+----------+
    |  4 | Chaitali |  25 | Mumbai  |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal  |  8500.00 |
    |  7 | Muffy    |  24 | Indore  | 10000.00 |
    +----+----------+-----+---------+----------+
    3 rows in set (0.00 sec)

假设变量 a 的值为 10，变量 b 的值为 20，那么：

操作符	描述	示例
=	检查两个操作数的值是否相等，是的话返回 true。	(a = b) 不为 true。
!=	检查两个操作数的值是否相等，如果不等则返回 true。	(a != b) 为 true。
	检查两个操作数的值是否相等，如果不等则返回 true。	(a b) 为真。
>	检查左边的操作数是否大于右边的操作数，是的话返回真。	(a > b) 不为 true。
	检查左边的操作数是否小于右边的操作数，是的话返回真。	(a
>=	检查左边的操作数是否大于或等于右边的操作数，是的话返回真。	(a >= b) 不为 true。
	检查左边的操作数是否小于或等于右边的操作数，是的话返回真。	(a
!	检查左边的操作数是否不小于右边的操作数，是的话返回真。	(a !
!>	检查左边的操作数是否不大于右边的操作数，是的话返回真。	(a !> b) 为 true。

SQL 逻辑运算符

考虑 CUSTOMERS 表，表中的记录如下所示：

    SQL> SELECT * FROM CUSTOMERS;
    +----+----------+-----+-----------+----------+
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
    |  3 | kaushik  |  23 | Kota      |  2000.00 |
    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  6 | Komal    |  22 | MP        |  4500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+
    7 rows in set (0.00 sec)

下面是一些关于如何使用 SQL 逻辑运算符的简单示例：

    SQL> SELECT * FROM CUSTOMERS WHERE AGE >= 25 AND SALARY >= 6500;
    +----+----------+-----+---------+---------+
    | ID | NAME     | AGE | ADDRESS | SALARY  |
    +----+----------+-----+---------+---------+
    |  4 | Chaitali |  25 | Mumbai  | 6500.00 |
    |  5 | Hardik   |  27 | Bhopal  | 8500.00 |
    +----+----------+-----+---------+---------+
    2 rows in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE AGE >= 25 OR SALARY >= 6500;
    +----+----------+-----+-----------+----------+
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+
    5 rows in set (0.00 sec)

    SQL>  SELECT * FROM CUSTOMERS WHERE AGE IS NOT NULL;
    +----+----------+-----+-----------+----------+
    | ID | NAME     | AGE | ADDRESS   | SALARY   |
    +----+----------+-----+-----------+----------+
    |  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
    |  2 | Khilan   |  25 | Delhi     |  1500.00 |
    |  3 | kaushik  |  23 | Kota      |  2000.00 |
    |  4 | Chaitali |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik   |  27 | Bhopal    |  8500.00 |
    |  6 | Komal    |  22 | MP        |  4500.00 |
    |  7 | Muffy    |  24 | Indore    | 10000.00 |
    +----+----------+-----+-----------+----------+
    7 rows in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE NAME LIKE 'Ko%';
    +----+-------+-----+---------+---------+
    | ID | NAME  | AGE | ADDRESS | SALARY  |
    +----+-------+-----+---------+---------+
    |  6 | Komal |  22 | MP      | 4500.00 |
    +----+-------+-----+---------+---------+
    1 row in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE AGE IN ( 25, 27 );
    +----+----------+-----+---------+---------+
    | ID | NAME     | AGE | ADDRESS | SALARY  |
    +----+----------+-----+---------+---------+
    |  2 | Khilan   |  25 | Delhi   | 1500.00 |
    |  4 | Chaitali |  25 | Mumbai  | 6500.00 |
    |  5 | Hardik   |  27 | Bhopal  | 8500.00 |
    +----+----------+-----+---------+---------+
    3 rows in set (0.00 sec)

    SQL> SELECT * FROM CUSTOMERS WHERE AGE BETWEEN 25 AND 27;
    +----+----------+-----+---------+---------+
    | ID | NAME     | AGE | ADDRESS | SALARY  |
    +----+----------+-----+---------+---------+
    |  2 | Khilan   |  25 | Delhi   | 1500.00 |
    |  4 | Chaitali |  25 | Mumbai  | 6500.00 |
    |  5 | Hardik   |  27 | Bhopal  | 8500.00 |
    +----+----------+-----+---------+---------+
    3 rows in set (0.00 sec)

    SQL> SELECT AGE FROM CUSTOMERS 
    WHERE EXISTS (SELECT AGE FROM CUSTOMERS WHERE SALARY > 6500);
    +-----+
    | AGE |
    +-----+
    |  32 |
    |  25 |
    |  23 |
    |  25 |
    |  27 |
    |  22 |
    |  24 |
    +-----+
    7 rows in set (0.02 sec)

    SQL> SELECT * FROM CUSTOMERS 
    WHERE AGE > ALL (SELECT AGE FROM CUSTOMERS WHERE SALARY > 6500);
    +----+--------+-----+-----------+---------+
    | ID | NAME   | AGE | ADDRESS   | SALARY  |
    +----+--------+-----+-----------+---------+
    |  1 | Ramesh |  32 | Ahmedabad | 2000.00 |
    +----+--------+-----+-----------+---------+
    1 row in set (0.02 sec)

    SQL> SELECT * FROM CUSTOMERS 
    WHERE AGE > ANY (SELECT AGE FROM CUSTOMERS WHERE SALARY > 6500);
    +----+----------+-----+-----------+---------+
    | ID | NAME     | AGE | ADDRESS   | SALARY  |
    +----+----------+-----+-----------+---------+
    |  1 | Ramesh   |  32 | Ahmedabad | 2000.00 |
    |  2 | Khilan   |  25 | Delhi     | 1500.00 |
    |  4 | Chaitali |  25 | Mumbai    | 6500.00 |
    |  5 | Hardik   |  27 | Bhopal    | 8500.00 |
    +----+----------+-----+-----------+---------+
    4 rows in set (0.00 sec)

下面列出了 SQL 中可用的逻辑运算符。

运算符	描述
ALL	ALL 运算符用于将一个值同另一个值集中所有的值进行比较。
AND	AND 运算符使得在 WHERE 子句中可以同时存在多个条件。
ANY	ANY 运算符用于将一个值同条件所指定的列表中的任意值相比较。
BETWEEN	给定最小值和最大值，BETWEEN 运算符可以用于搜索区间内的值。
EXISTS	EXISTS 运算符用于在表中搜索符合特定条件的行。
IN	IN 运算符用于将某个值同指定的一列字面值相比较。
LIKE	LIKE 运算符用于使用通配符对某个值和与其相似的值做出比较。
NOT	NOT 操作符反转它所作用的操作符的意义。例如，NOT EXISTS、NOT BETWEEN、NOT IN 等。这是一个求反运算符。
OR	OR 运算符用于在 SQL 语句中连接多个条件。
IS NULL	NULL Operator 用于将某个值同 NULL 作比较。
UNIQUE	UNIQUE 运算符检查指定表的所有行，以确定没有重复。