sql必知必会笔记

distinct:

只返回不同值的行（返回结果不会重复）；

示例：

没有使用distinct的结果：

mysql> select vend_id from products;
+---------+
| vend_id |
+---------+
|    1001 |
|    1001 |
|    1001 |
|    1002 |
|    1002 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1003 |
|    1005 |
|    1005 |
+---------+
14 rows in set (0.00 sec)

使用distinct的结果：

mysql> select distinct vend_id from products;
+---------+
| vend_id |
+---------+
|    1001 |
|    1002 |
|    1003 |
|    1005 |
+---------+
4 rows in set (0.00 sec)

---

注释：/* */  or  #

mysql> select * from products /*annotation*/
    -> #anotation;
    -> ;

order by 列名：默认升序排列

mysql> select prod_name,prod_price from products order by prod_price;
+----------------+------------+
| prod_name      | prod_price |
+----------------+------------+
| TNT (1 stick)  |       2.50 |
| Carrots        |       2.50 |
| Fuses          |       3.42 |
| Sling          |       4.49 |
| .5 ton anvil   |       5.99 |
| Oil can        |       8.99 |
| 1 ton anvil    |       9.99 |
| TNT (5 sticks) |      10.00 |
| Bird seed      |      10.00 |
| Detonator      |      13.00 |
| 2 ton anvil    |      14.99 |
| JetPack 1000   |      35.00 |
| Safe           |      50.00 |
| JetPack 2000   |      55.00 |
+----------------+------------+
14 rows in set (0.00 sec)

order by 列名 desc:降序排列

mysql> select prod_name,prod_price from products order by prod_price desc;
+----------------+------------+
| prod_name      | prod_price |
+----------------+------------+
| JetPack 2000   |      55.00 |
| Safe           |      50.00 |
| JetPack 1000   |      35.00 |
| 2 ton anvil    |      14.99 |
| Detonator      |      13.00 |
| TNT (5 sticks) |      10.00 |
| Bird seed      |      10.00 |
| 1 ton anvil    |       9.99 |
| Oil can        |       8.99 |
| .5 ton anvil   |       5.99 |
| Sling          |       4.49 |
| Fuses          |       3.42 |
| Carrots        |       2.50 |
| TNT (1 stick)  |       2.50 |
+----------------+------------+
14 rows in set (0.00 sec)

---

AND：与

mysql> select prod_id from products where prod_id='ANV01' and vend_id=1001;
+---------+
| prod_id |
+---------+
| ANV01   |
+---------+
1 row in set (0.00 sec)

or：或

mysql> select prod_id from products where prod_id='ANV01' or vend_id=1001;
+---------+
| prod_id |
+---------+
| ANV01   |
| ANV02   |
| ANV03   |
+---------+
3 rows in set (0.00 sec)

in : 在（value1，vlaue2,value3，...）

 

mysql> select prod_id,prod_name,prod_price from products where vend_id in (1001,1003);
+---------+----------------+------------+
| prod_id | prod_name      | prod_price |
+---------+----------------+------------+
| ANV01   | .5 ton anvil   |       5.99 |
| ANV02   | 1 ton anvil    |       9.99 |
| ANV03   | 2 ton anvil    |      14.99 |
| DTNTR   | Detonator      |      13.00 |
| FB      | Bird seed      |      10.00 |
| FC      | Carrots        |       2.50 |
| SAFE    | Safe           |      50.00 |
| SLING   | Sling          |       4.49 |
| TNT1    | TNT (1 stick)  |       2.50 |
| TNT2    | TNT (5 sticks) |      10.00 |
+---------+----------------+------------+
10 rows in set (0.00 sec)

 

not：不等于（此条示例也可以用！=实现）

mysql> select * from products where not vend_id=1001;
+---------+---------+----------------+------------+-------------------------------------------------+
| prod_id | vend_id | prod_name      | prod_price | prod_desc                                       |
+---------+---------+----------------+------------+-------------------------------------------------+
| DTNTR   |    1003 | Detonator      |      13.00 | Detonator (plunger powered), fuses not included |
| FB      |    1003 | Bird seed      |      10.00 | Large bag (suitable for road runners)           |
| FC      |    1003 | Carrots        |       2.50 | Carrots (rabbit hunting season only)            |
| FU1     |    1002 | Fuses          |       3.42 | 1 dozen, extra long                             |
| JP1000  |    1005 | JetPack 1000   |      35.00 | JetPack 1000, intended for single use           |
| JP2000  |    1005 | JetPack 2000   |      55.00 | JetPack 2000, multi-use                         |
| OL1     |    1002 | Oil can        |       8.99 | Oil can, red                                    |
| SAFE    |    1003 | Safe           |      50.00 | Safe with combination lock                      |
| SLING   |    1003 | Sling          |       4.49 | Sling, one size fits all                        |
| TNT1    |    1003 | TNT (1 stick)  |       2.50 | TNT, red, single stick                          |
| TNT2    |    1003 | TNT (5 sticks) |      10.00 | TNT, red, pack of 10 sticks                     |
+---------+---------+----------------+------------+-------------------------------------------------+
11 rows in set (0.00 sec)

百分号（%）通配符：代表匹配0，1或多个字符

mysql> select * from products where vend_id like "%03";
+---------+---------+----------------+------------+-------------------------------------------------+
| prod_id | vend_id | prod_name      | prod_price | prod_desc                                       |
+---------+---------+----------------+------------+-------------------------------------------------+
| DTNTR   |    1003 | Detonator      |      13.00 | Detonator (plunger powered), fuses not included |
| FB      |    1003 | Bird seed      |      10.00 | Large bag (suitable for road runners)           |
| FC      |    1003 | Carrots        |       2.50 | Carrots (rabbit hunting season only)            |
| SAFE    |    1003 | Safe           |      50.00 | Safe with combination lock                      |
| SLING   |    1003 | Sling          |       4.49 | Sling, one size fits all                        |
| TNT1    |    1003 | TNT (1 stick)  |       2.50 | TNT, red, single stick                          |
| TNT2    |    1003 | TNT (5 sticks) |      10.00 | TNT, red, pack of 10 sticks                     |
+---------+---------+----------------+------------+-------------------------------------------------+
7 rows in set (0.00 sec)

mysql> select * from products where vend_id like
    -> '%ton anvi%';
Empty set (0.00 sec)

mysql> select * from products where prod_name like '%vil';
+---------+---------+--------------+------------+----------------------------------------------------------------+
| prod_id | vend_id | prod_name    | prod_price | prod_desc                                                      |
+---------+---------+--------------+------------+----------------------------------------------------------------+
| ANV01   |    1001 | .5 ton anvil |       5.99 | .5 ton anvil, black, complete with handy hook                  |
| ANV02   |    1001 | 1 ton anvil  |       9.99 | 1 ton anvil, black, complete with handy hook and carrying case |
| ANV03   |    1001 | 2 ton anvil  |      14.99 | 2 ton anvil, black, complete with handy hook and carrying case |
+---------+---------+--------------+------------+----------------------------------------------------------------+
3 rows in set (0.00 sec)

select * from products where prod_name like '%';  

不会匹配prod_name为null的行；

 下划线  “_” ：匹配一个字符

mysql> select * from products where prod_name like '_ ton anvil';
+---------+---------+-------------+------------+----------------------------------------------------------------+
| prod_id | vend_id | prod_name   | prod_price | prod_desc                                                      |
+---------+---------+-------------+------------+----------------------------------------------------------------+
| ANV02   |    1001 | 1 ton anvil |       9.99 | 1 ton anvil, black, complete with handy hook and carrying case |
| ANV03   |    1001 | 2 ton anvil |      14.99 | 2 ton anvil, black, complete with handy hook and carrying case |
+---------+---------+-------------+------------+----------------------------------------------------------------+
2 rows in set (0.00 sec)

使用concat()函数对查询结果进行拼接：

mysql> select concat(cust_id,'==',cust_name) from customers;
+--------------------------------+
| concat(cust_id,'==',cust_name) |
+--------------------------------+
| 10001==Coyote Inc.             |
| 10002==Mouse House             |
| 10003==Wascals                 |
| 10004==Yosemite Place          |
| 10005==E Fudd                  |
+--------------------------------+
5 rows in set (0.00 sec)