mysql - 是否可以组合这些 SQL select 语句？

Question

我正在使用 mysql/mariadb。

我想做的:为每个 Group 获取 id、name、private/然后获取每个 Group 中的 Video 数量/然后为每个 Group 获取最后 20 个 Video。

现在，我使用三个单独的 SQL 查询，然后每次都针对每个相应的 ID 运行它。有没有办法将三个 SQL 查询合并为一个，并在一个 ID 列表上运行它们？

例如，在组 1、2、3 上:

Executing (default): select `id`, `name`, `private` from `Groups` where `id` = '1' limit 1
Executing (default): select `id`, `name`, `private` from `Groups` where `id` = '2' limit 1
Executing (default): select `id`, `name`, `private` from `Groups` where `id` = '3' limit 1

Executing (default): select count(*) from `Videos` where `GroupId` = '1' and `live` = true
Executing (default): select count(*) from `Videos` where `GroupId` = '2' and `live` = true
Executing (default): select count(*) from `Videos` where `GroupId` = '3' and `live` = true

Executing (default): select `id`, `file` from `Videos` where `GroupId` = '1' and `live` = true order by `id` desc limit 20
Executing (default): select `id`, `file` from `Videos` where `GroupId` = '2' and `live` = true order by `id` desc limit 20
Executing (default): select `id`, `file` from `Videos` where `GroupId` = '3' and `live` = true order by `id` desc limit 20

Answer 1

使用 IN

Executing (default): (SELECT `id`, `name`, `private` FROM `Groups` WHERE`id` = '1' LIMIT 1)
                     UNION ALL
                     (SELECT `id`, `name`, `private` FROM `Groups` WHERE`id` = '2' LIMIT 1)
                     UNION ALL
                     (SELECT `id`, `name`, `private` FROM `Groups` WHERE`id` = '3' LIMIT 1)

Executing (default): SELECT count(*) 
                     FROM `Videos` 
                     WHERE `GroupId` IN ('1', '2', '3')  AND `live` = true

Executing (default): (SELECT `id`, `file` FROM `Videos` WHERE`GroupId` = '1' AND `live` = true ORDER BY `id` DESC LIMIT 20)
                     UNION ALL
                     (SELECT `id`, `file` FROM `Videos` WHERE`GroupId` = '2' AND `live` = true ORDER BY `id` DESC LIMIT 20)
                     UNION ALL
                     (SELECT `id`, `file` FROM `Videos` WHERE`GroupId` = '3' AND `live` = true ORDER BY `id` DESC LIMIT 20)