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。
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 |
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。 |
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。 |
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