mysql - 根据 mysql 列和组结果增加一个值或另一个值

Question

我有 table1(id, name), table2(id [FK to table1.id],user_id,visit)。对于每个table1.id，我需要从table1显示它的名称，计算用户并显示他们属于这个id的user_id，当table2.visit=1时，计算用户并显示他们属于这个id的user_id，当table2.visit= 0。此外，table1 中的某些 id 可能在 table2 中不存在，对于这些 id，我希望在计数器中有 0。

结果表应如下所示：

id|name|count_visitors|list_of_visitors_id|count_non_visitors|list_of_non_visitors_id|
1 |a   |2             |5,10               |1                 |4                      |

你能帮忙查询一下吗？

Answer 1

SELECT t1.name, 
       COALESCE( visitors.visitors_count, 0) AS `count_visitors`,
       COALESCE( visitors.visitors_list, '') AS `list_of_visitors_id`, 
       COALESCE( nonvisitors.nonvisitors_count, 0 ) AS `count_non_visitors`,
       COALESCE( nonvisitors.nonvisitors_list, '') AS `list_of_non_visitors_id`
FROM table1 t1
LEFT JOIN
( SELECT id, GROUP_CONCAT( user_id ) AS visitors_list, COUNT(*) AS visitors_count
    FROM table2
    WHERE visit = 1
    GROUP BY id ) visitors
ON t1.id = visitors.id
LEFT JOIN
  ( SELECT id, GROUP_CONCAT( user_id ) AS nonvisitors_list, COUNT(*) AS nonvisitors_count
    FROM table2
    WHERE visit = 0
    GROUP BY id ) nonvisitors
ON t1.id = nonvisitors.id

自己试试：Sqlfiddle

如果您需要一位用户使用它，只需在末尾添加一行：

WHERE t1.id = 1