仅当两个或多个记录具有相同值时才连接两个表并分组

Question

我有 2 个表：

manifests
id | customer | paid_order | price | payment_method

paid_orders
id | paid

JOIN paid_orders ON manifests.paid_order = paid_order_id

Let's assume this scenario:
There are 2 same customer but has different payment_method.

customer | paid_order | price | payment_method |  paid  |
    1    |      1     | 200   |        0       |  200   |
    1    |     NULL   | 100   |        1       |  NULL  |
    2    |     NULL   | 150   |        1       |  NULL  |

我只想GROUP BY customer而且PICK只有0的payment_method只有如果有两个相同的客户。

预期结果：

customer | paid_order | price | payment_method |  paid  |
    1    |      1     | 200   |        0       |  200   |
    2    |     NULL   | 150   |        1       |  NULL  |

Answer 1

一种方法是始终 select 来自一个或多个客户记录的记录，其中 payment_method 具有最小值：

SELECT m1.*
FROM manifest m1
INNER JOIN
(
    SELECT customer, MIN(payment_method) AS min_payment_method
    FROM manifest
    GROUP BY customer
) m2
    ON m1.customer = m2.customer AND m1.payment_method = m2.min_payment_method;

这个逻辑应该有效，因为如果 payment_method 为零，那么这条记录将成为目标。否则，将针对一个值记录。

仅当两个或多个记录具有相同值时才连接两个表并分组

joining two tables and grouping only if two or more records has same value

mysql

relational-database