SQL TOP LIMIT 和 ROWNUM

SQL TOP语句用于从表中获取前 N 个或 X% 的记录。

注意- 所有数据库都不支持 TOP 子句。例如 MySQL 支持LIMIT语句来获取有限数量的记录，而 Oracle 使用ROWNUM命令来获取有限数量的记录。

语法

带有 SELECT 语句的 TOP 子句的基本语法如下。

SELECT TOP number|percent column_name(s)
FROM table_name
WHERE [condition]

示例

CUSTOMERS 表

+----+----------+-----+-----------+----------+
| 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 |
+----+----------+-----+-----------+----------+

以下示例将从 CUSTOMERS 表中获取前 3 条记录。

SQL> SELECT TOP 3 * FROM CUSTOMERS;

结果如下

+----+---------+-----+-----------+---------+
| ID | NAME    | AGE | ADDRESS   | SALARY  |
+----+---------+-----+-----------+---------+
|  1 | Ramesh  |  32 | Ahmedabad | 2000.00 |
|  2 | Khilan  |  25 | Delhi     | 1500.00 |
|  3 | kaushik |  23 | Kota      | 2000.00 |
+----+---------+-----+-----------+---------+

如果使用的是 MySQL 服务器，那么需要使用下面的sql语句实现该效果

SQL> SELECT * FROM CUSTOMERS
LIMIT 3;

结果如下

+----+---------+-----+-----------+---------+
| ID | NAME    | AGE | ADDRESS   | SALARY  |
+----+---------+-----+-----------+---------+
|  1 | Ramesh  |  32 | Ahmedabad | 2000.00 |
|  2 | Khilan  |  25 | Delhi     | 1500.00 |
|  3 | kaushik |  23 | Kota      | 2000.00 |
+----+---------+-----+-----------+---------+

如果使用的是 Oracle 服务器，那么需要使用下面的sql语句实现该效果。

SQL> SELECT * FROM CUSTOMERS
WHERE ROWNUM <= 3;

结果如下

+----+---------+-----+-----------+---------+
| ID | NAME    | AGE | ADDRESS   | SALARY  |
+----+---------+-----+-----------+---------+
|  1 | Ramesh  |  32 | Ahmedabad | 2000.00 |
|  2 | Khilan  |  25 | Delhi     | 1500.00 |
|  3 | kaushik |  23 | Kota      | 2000.00 |
+----+---------+-----+-----------+---------+