MySQL检索和过滤数据
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注意
- 多条SQL语句必须以分号（；）分隔；
- SQL语句不区分大小写；
- 在处理SQL语句时，其中所有空格都被忽略；
- 当选择多个列是，一定要在列名之间加上逗号，但最后一个列名后不加。
SELECT语句
检索单个列
mysql> SELECT prod_name FROM products;
+----------------+
| 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) |
+----------------+
14 rows in set (0.00 sec)
检索所有列
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 |
+---------+---------+----------------+------------+----------------------------------------------------------------+
14 rows in set (0.00 sec)
检索不同行
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)
去重
mysql> SELECT DISTINCT vend_id FROM products;
+---------+
| vend_id |
+---------+
| 1001 |
| 1002 |
| 1003 |
| 1005 |
+---------+
4 rows in set (0.00 sec)
- DISTINCT关键字，应用于所有列而不是前置它的列。
限制结果
mysql> SELECT vend_id FROM products LIMIT 5,5;
+---------+
| vend_id |
+---------+
| 1003 |
| 1003 |
| 1003 |
| 1003 |
| 1003 |
+---------+
5 rows in set (0.00 sec)
- LIMIT 5,5 指示MySQL返回从行5开始的5行。
ORDER BY子句
单个排序
mysql> SELECT prod_name FROM products ORDER BY prod_name;
+----------------+
| prod_name |
+----------------+
| .5 ton anvil |
| 1 ton anvil |
| 2 ton anvil |
| Bird seed |
| Carrots |
| Detonator |
| Fuses |
| JetPack 1000 |
| JetPack 2000 |
| Oil can |
| Safe |
| Sling |
| TNT (1 stick) |
| TNT (5 sticks) |
+----------------+
14 rows in set (0.00 sec)
多个列排序
mysql> SELECT prod_id,prod_price,prod_name FROM products ORDER BY prod_price,prod_name;
+---------+------------+----------------+
| prod_id | prod_price | prod_name |
+---------+------------+----------------+
| FC | 2.50 | Carrots |
| TNT1 | 2.50 | TNT (1 stick) |
| FU1 | 3.42 | Fuses |
| SLING | 4.49 | Sling |
| ANV01 | 5.99 | .5 ton anvil |
| OL1 | 8.99 | Oil can |
| ANV02 | 9.99 | 1 ton anvil |
| FB | 10.00 | Bird seed |
| TNT2 | 10.00 | TNT (5 sticks) |
| DTNTR | 13.00 | Detonator |
| ANV03 | 14.99 | 2 ton anvil |
| JP1000 | 35.00 | JetPack 1000 |
| SAFE | 50.00 | Safe |
| JP2000 | 55.00 | JetPack 2000 |
+---------+------------+----------------+
14 rows in set (0.00 sec)
- 对于上述例子中的输出，仅在多个行具有相同的prod_price值时才对产品按prod_name进行排序。如果prod_price列中所有的值都是唯一的，则不会按prod_name排序。
指定排序方向
mysql> SELECT prod_id,prod_price,prod_name FROM products ORDER BY prod_price,prod_name,prod_name;
+---------+------------+----------------+
| prod_id | prod_price | prod_name |
+---------+------------+----------------+
| FC | 2.50 | Carrots |
| TNT1 | 2.50 | TNT (1 stick) |
| FU1 | 3.42 | Fuses |
| SLING | 4.49 | Sling |
| ANV01 | 5.99 | .5 ton anvil |
| OL1 | 8.99 | Oil can |
| ANV02 | 9.99 | 1 ton anvil |
| FB | 10.00 | Bird seed |
| TNT2 | 10.00 | TNT (5 sticks) |
| DTNTR | 13.00 | Detonator |
| ANV03 | 14.99 | 2 ton anvil |
| JP1000 | 35.00 | JetPack 1000 |
| SAFE | 50.00 | Safe |
| JP2000 | 55.00 | JetPack 2000 |
+---------+------------+----------------+
14 rows in set (0.00 sec)
- 默认是顺序排序（ASC）；
- 如果要逆序就在需要逆序的列指定DESC。
WHERE 子句
WHERE 子句操作符
| 操 作 符 | 说 明 |
|---|---|
| = | 等于 |
| <> | 不等于 |
| ！= | 不等于 |
| < | 小于 |
| <= | 小于等于 |
| > | 大于 |
| >= | 大于等于 |
| = | 等于 |
| BETWEEN | 在指定的两个值之间 |
检查单个值
mysql> SELECT prod_id,prod_price,prod_name FROM products WHERE prod_name=‘fuses‘;
+---------+------------+-----------+
| prod_id | prod_price | prod_name |
+---------+------------+-----------+
| FU1 | 3.42 | Fuses |
+---------+------------+-----------+
1 row in set (0.00 sec)
不破配检查
mysql> SELECT vend_id,prod_name FROM products WHERE vend_id <> 1003;
+---------+--------------+
| vend_id | prod_name |
+---------+--------------+
| 1001 | .5 ton anvil |
| 1001 | 1 ton anvil |
| 1001 | 2 ton anvil |
| 1002 | Fuses |
| 1002 | Oil can |
| 1005 | JetPack 1000 |
| 1005 | JetPack 2000 |
+---------+--------------+
7 rows in set (0.01 sec)
范围值检查
mysql> SELECT vend_id,prod_name FROM products WHERE prod_price BETWEEN 5 AND 10;
+---------+----------------+
| vend_id | prod_name |
+---------+----------------+
| 1001 | .5 ton anvil |
| 1001 | 1 ton anvil |
| 1003 | Bird seed |
| 1002 | Oil can |
| 1003 | TNT (5 sticks) |
+---------+----------------+
5 rows in set (0.01 sec)
空值检查
mysql> SELECT cust_id FROM customers WHERE cust_email IS NULL;
+---------+
| cust_id |
+---------+
| 10002 |
| 10005 |
+---------+
2 rows in set (0.00 sec)
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