在Mysql使用过程中经常会limit来获取特定的范围的row数据，其中常用的两种用法。
limit是对Mysql查询结果进行分割（或者分页）返回
第一：limit num；
下方是详细讲解的例子：
mysql> SELECT * FROM ratings ORDER BY category;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
| 1 | 1 | 4.5 |
| 5 | 1 | 3.2 |
| 3 | 2 | 3.7 |
| 4 | 2 | 3.5 |
| 6 | 2 | 3.5 |
| 2 | 3 | 5.0 |
| 7 | 3 | 2.7 |
+----+----------+--------+
使用limit：
mysql> SELECT * FROM ratings ORDER BY category LIMIT 5;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
| 1 | 1 | 4.5 |
| 5 | 1 | 3.2 |
| 4 | 2 | 3.5 |
| 3 | 2 | 3.7 |
| 6 | 2 | 3.5 |
+----+----------+--------+
第二：limit x,y;
举例：
mysql> SELECT * FROM ratings ORDER BY category;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
| 1 | 1 | 4.5 |
| 5 | 1 | 3.2 |
| 3 | 2 | 3.7 |
| 4 | 2 | 3.5 |
| 6 | 2 | 3.5 |
| 2 | 3 | 5.0 |
| 7 | 3 | 2.7 |
+----+----------+--------+
1.LIMIT表示分页查询， LIMIT 0,4; 表示从索引为0的位置，就是第一个往后查4条数据。
mysql> SELECT * FROM ratings ORDER BY category LIMIT 0, 4;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
| 1 | 1 | 4.5 |
| 5 | 1 | 3.2 |
| 4 | 2 | 3.5 |
| 3 | 2 | 3.7 |
+----+----------+--------+
- LIMIT 3,3; 表示从索引为4的位置也就是第五条开始往后查8条数据。
mysql> SELECT * FROM ratings ORDER BY category LIMIT 3, 3;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
| 4 | 2 | 3.5 |
| 6 | 2 | 3.5 |
| 2 | 3 | 5.0 |
+----+----------+--------+
总结：limit 是用于对返回数据的分割（分页）。