希望通过合并这些查询在一个查询中获得两个查询的结果

Question

所以，我有两个表，一个是 A(order_id, order_group_id, name)，第二个是 B(order_group_id, paid)。

表A有几条记录：

order_id | order_group_id | name
----------------------------------
1        | 0              | A
----------------------------------
2        | 14             | B
----------------------------------
3        | 0              | C
----------------------------------
4        | 15             | D

表B有几条记录：

order_group_id | paid
--------------------------
14             | 0              
--------------------------
15             | 1

现在我正在运行这两个查询：

SELECT order_id FROM A WHERE order_group_id = 0

和

SELECT d.order_id FROM A as d, B as e WHERE d.order_group_id = e.order_group_id AND e.paid = 0

第一个查询给出order_id 1和3 。

第二个查询给出order_id 2 。

那么，现在如何在一个查询中获得这两个查询的结果，这些order_id也应该按升序排列。

Answer 1

您可以使用LEFT JOIN实现它

此查询将返回所有paid is 0或order_group_id is 0的记录

SELECT order_id, e.paid,  d.order_group_id FROM A as d
LEFT JOIN B as e ON d.order_group_id = e.order_group_id
WHERE e.paid = 0 OR d.order_group_id = 0

在codeignitor中，您可以通过以下方式实现

$query = $this->select('SELECT order_id, e.paid,  d.order_group_id')->from('A as d')->join('B as e','d.order_group_id = e.order_group_id','LEFT')->where('e.paid = 0 OR d.order_group_id = 0')->get();

演示： http ://sqlfiddle.com/#!9/2b82f9/8

Answer 2

SELECT order_id FROM A WHERE order_group_id = 0
union
SELECT d.order_id FROM A as d, B as e WHERE d.order_group_id = e.order_group_id AND e.paid = 0

Answer 3

您可以使用 INNER JOIN 关联两个或多个表。 并使用 ORDER BY (column) ASC/DESC 进行升序或降序

SELECT order_id FROM A as d INNER JOIN B as e 
ON d.order_group_id = e.order_group_id
WHERE d.order_group_id = 0 AND e.paid = 0
ORDER BY order_id ASC