MySQL学习足迹记录02--SELECT

本查询所用到的表格结构和数据

mysql> SHOW COLUMNS FROM products;

+------------+--------------+------+-----+---------+-------+

| Field | Type | Null | Key | Default | Extra |

+------------+--------------+------+-----+---------+-------+

| prod_id | char(10) | NO | PRI | NULL | |

| vend_id | int(11) | NO | MUL | NULL | |

| prod_name | char(255) | NO | | NULL | |

| prod_price | decimal(8,2) | NO | | NULL | |

| prod_desc | text | YES | | NULL | |

+------------+--------------+------+-----+---------+-------+

mysql>
select * from products;

+---------+---------+----------------+------------+----------------------------------------------------------------+

| 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 |

| 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 |

+---------+---------+----------------+------------+----------------------------------------------------------------+

1.检索单个列：

eg:

mysql> SELECT prod_NAME
FROM products; #MYSQL并不区分大小写

+----------------+

| prod_NAME |

+----------------+

| .5 ton anvil |

| 1 ton anvil |

| 2 ton anvil |

| Detonator |

| Bird seed |

| Carrots |

| Fuses |

| JetPack 1000 |

| JetPack 2000 |

| Oil can |

| Safe |

| Sling |

| TNT (1 stick) |

| TNT (5 sticks) |

+----------------+

2.检索多个列

eg:

mysql> SELECT prod_id,prod_name,prod_price FROM products;

+---------+----------------+------------+

| 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 |

| FU1 | Fuses | 3.42 |

| JP1000 | JetPack 1000 | 35.00 |

| JP2000 | JetPack 2000 | 55.00 |

| OL1 | Oil can | 8.99 |

| SAFE | Safe | 50.00 |

| SLING | Sling | 4.49 |

| TNT1 | TNT (1 stick) | 2.50 |

| TNT2 | TNT (5 sticks) | 10.00 |

+---------+----------------+------------+

3.检索所有列

eg:

mysql>
SELECT * FROM products;

+---------+---------+----------------+------------+----------------------------------------------------------------+

| 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 |

| 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 |

+---------+---------+----------------+------------+----------------------------------------------------------------+

4.检索不同的行

先列出所有的行以便作对比

eg:

mysql>
SELECT vend_id FROM products;

+---------+

| vend_id |

+---------+

| 1001 |

| 1001 |

| 1001 |

| 1002 |

| 1002 |

| 1003 |

| 1003 |

| 1003 |

| 1003 |

| 1003 |

| 1003 |

| 1003 |

| 1005 |

| 1005 |

+---------+

*DISTINGCT关键字便可以把相同的行去掉

mysql>
SELECT DISTINCT vend_id FROM products;

+---------+

| vend_id |

+---------+

| 1001 |

| 1002 |

| 1003 |

| 1005 |

+---------+

5.限制结果

*限制返回前几行

eg:

mysql>
SELECT prod_name FROM products LIMIT 5;

+--------------+

| prod_name |

+--------------+

| .5 ton anvil |

| 1 ton anvil |

| 2 ton anvil |

| Detonator |

| Bird seed |

+--------------+

*限制返回从从第N行开始（下标从0开始），一直持续M行结束

eg:

mysql>
SELECT prod_name FROM products LIMIT 5,5;

+--------------+

| prod_name |

+--------------+

| Carrots |

| Fuses |

| JetPack 1000 |

| JetPack 2000 |

| Oil can |

+--------------+

6.使用完全限定的表名

eg:

mysql>
SELECT products.prod_name FROM MySQL_ex.products; #products为表名，MySQL_ex为数据库名



+----------------+

| prod_name |

+----------------+

| .5 ton anvil |

| 1 ton anvil |

| 2 ton anvil |

| Detonator |

| Bird seed |

| Carrots |

| Fuses |

| JetPack 1000 |

| JetPack 2000 |

| Oil can |

| Safe |

| Sling |

| TNT (1 stick) |

| TNT (5 sticks) |

+----------------+