mysql必知必会 （二）排序数据（order by）

按一列排序

mysql> select prod_name
    -> from products
    -> order by prod_name;
+---------------------+
| prod_name           |
+---------------------+
| 12 inch teddy bear  |
| 18 inch teddy bear  |
| 8 inch teddy bear   |
| Bird bean bag toy   |
| Fish bean bag toy   |
| King doll           |
| Queen doll          |
| Rabbit bean bag toy |
| Raggedy Ann         |
+---------------------+
9 rows in set (0.00 sec)

按多列排序

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by prod_price, prod_name;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
| RGAN01  |       4.99 | Raggedy Ann         |
| BR01    |       5.99 | 8 inch teddy bear   |
| BR02    |       8.99 | 12 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR03    |      11.99 | 18 inch teddy bear  |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

指定排序方向：desc

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by prod_price desc;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BR03    |      11.99 | 18 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR02    |       8.99 | 12 inch teddy bear  |
| BR01    |       5.99 | 8 inch teddy bear   |
| RGAN01  |       4.99 | Raggedy Ann         |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

mysql> select prod_id, prod_price, prod_name
    -> from products
    -> order by prod_price desc, prod_name;
+---------+------------+---------------------+
| prod_id | prod_price | prod_name           |
+---------+------------+---------------------+
| BR03    |      11.99 | 18 inch teddy bear  |
| RYL01   |       9.49 | King doll           |
| RYL02   |       9.49 | Queen doll          |
| BR02    |       8.99 | 12 inch teddy bear  |
| BR01    |       5.99 | 8 inch teddy bear   |
| RGAN01  |       4.99 | Raggedy Ann         |
| BNBG02  |       3.49 | Bird bean bag toy   |
| BNBG01  |       3.49 | Fish bean bag toy   |
| BNBG03  |       3.49 | Rabbit bean bag toy |
+---------+------------+---------------------+
9 rows in set (0.00 sec)

可见desc只作用于其前面的1列，而之前的distinct会作用于其后的所有列

limit和order by组合

选出最大值

mysql> select prod_price
    -> from products
    -> order by prod_price desc
    -> limit 1;
+------------+
| prod_price |
+------------+
|      11.99 |
+------------+
1 row in set (0.00 sec)

返回最大的前4个

mysql> select prod_price
    -> from products
    -> order by prod_price desc
    -> limit 4;
+------------+
| prod_price |
+------------+
|      11.99 |
|       9.49 |
|       9.49 |
|       8.99 |
+------------+

总结

• order by子句必须在from子句后面；limit子句必须在order by子句后面