SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5;
SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_price,prod_id FROM products WHERE vend_id IN (1001,1002);
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION ALL SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002) ORDER BY vend_id,prod_price;
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 OR vend_id IN (1001,1002);
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5;
| vend_id | prod_id | prod_price |
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1003 | SLING | 4.49 |
| 1003 | TNT1 | 2.50 |
SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
| vend_id | prod_id | prod_price |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1002 | FU1 | 3.42 |
| 1002 | OL1 | 8.99 |
使用组合查询：UNION
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
| vend_id | prod_id | prod_price |
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1003 | SLING | 4.49 |
| 1003 | TNT1 | 2.50 |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1002 | OL1 | 8.99 |
使用多个where条件：
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 OR vend_id IN (1001,1002);
| vend_id | prod_id | prod_price |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1002 | OL1 | 8.99 |
| 1003 | SLING | 4.99 |
| 1003 | TNT1 | 2.50 |
关于组合查询（UNION）：各个查询包含的列、表达式、聚集函数必须相同，对各列的次序没有要求，不过最好次序一致。
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_price,prod_id FROM products WHERE vend_id IN (1001,1002);
| vend_id | prod_id | prod_price |
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1003 | SLING | 4.49 |
| 1003 | TNT1 | 2.50 |
| 1001 | 5.99 | ANV01 |
| 1001 | 9.99 | ANV02 |
| 1001 | 14.99 | ANV03 |
| 1002 | 3.42 | FU1 |
| 1002 | 8.99 | OL1 |
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION ALL SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002);
| vend_id | prod_id | prod_price |
| 1003 | FC | 2.50 |
| 1002 | FU1 | 3.42 |
| 1003 | SLING | 4.49 |
| 1003 | TNT1 | 2.50 |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1002 | FU1 | 3.42 |
| 1002 | OL1 | 8.99 |
SELECT vend_id,prod_id,prod_price FROM products WHERE prod_price<=5 UNION SELECT vend_id,prod_id,prod_price FROM products WHERE vend_id IN (1001,1002) ORDER BY vend_id,prod_price;
| vend_id | prod_id | prod_price |
| 1001 | ANV01 | 5.99 |
| 1001 | ANV02 | 9.99 |
| 1001 | ANV03 | 14.99 |
| 1002 | FU1 | 3.42 |
| 1002 | OL1 | 8.99 |
| 1003 | TNT1 | 2.50 |
| 1003 | FC | 2.50 |
| 1003 | SLING | 4.49 |
关于组合查询(UNION/UNION ALL)：
各个查询包含的列、表达式、聚集函数必须相同，不过对各列次序没有要求，当然，最好次序相同。
使用组合查询(UNION)， 会默认去除重复行。
使用组合查询(UNION ALL)，不会去除重复行
关于组合查询的排序关于UNION / UNION ALL 的 ORDER BY)：
组合查询中只能使用一个ORDER BY，且必须放在最后一个SELECT子句后
ORDER BY 是对所有SELECT 的结果进行排序。