Question

我需要将以下三个SELECT语句合并为一个SQL语句：

1. SELECT TotalTime FROM Session WHERE device_uid = ${my_uid} ORDER BY StartTime DESC LIMIT 1;

2. SELECT HoursAtService FROM Service WHERE device_uid = ${my_uid} ORDER BY StartTime DESC LIMIT 1;

3. SELECT ServiceHours FROM Type WHERE type_uid = ${my_type_uid};

最好，我希望将结果作为一行包含以下字段：

Result:
----------------------------------------------------------------
uid, TotalTime, HoursAtService, ServiceHours

我正在考虑可能需要进行内部联接，但是我不确定100％如何进行内部联接。像这样：

SELECT uid, TotalTime, HoursAtService, ServiceHours FROM Device AS t1 INNER JOIN (... -> continues

在表之间进行联接很容易，但是如何对多个表使用多个WHERE子句进行联接？

有人可以告诉我如何构造查询吗？

编辑-表模式

Device:
---------------------
device_uid, type_uid, ....

Session:
---------------------
device_uid, session_uid, TotalTime, StartTime, EndTime, SessionTime

Service:
---------------------
device_uid, service_uid, StartTime, EndTime, HoursAtService

Type:
---------------------
type_uid, Name, ServiceHours

Answer 1

您可以在单个查询中合并上面的单个查询，例如在MYSQL查询下面：

SELECT Session.uid, Session.TotalTime, Service.HoursAtService, ServiceHours.ServiceHours
FROM Session 
JOIN Service ON Service.udi = Session.uid
JOIN ServiceHours ON ServiceHours.type_uid = Session.uid
WHERE Session.uid = ${my_uid}
ORDER BY Session.StartTime DESC LIMIT 1;

更改相关表中的列名。

Answer 2

尝试这样的事情：

SELECT ${my_uid} AS uid,
       (SELECT TotalTime FROM Session WHERE uid = ${my_uid} ORDER BY StartTime DESC LIMIT 1) AS TotalTime,
       (SELECT HoursAtService FROM Service WHERE udi = ${my_uid} ORDER BY StartTime DESC LIMIT 1) AS HoursAtService,
       (SELECT ServiceHours FROM Type WHERE type_uid = ${my_type_uid) AS ServiceHours

Answer 3

您可以使用以下查询来实现您提到的内容，由于服务和会话都是SQL关键字，因此我也考虑了关键字的方括号。

SELECT 
    [Device].Type_uid AS DeviceTypeId, [Device].Device_uid AS DeviceId, [Session].TotalTime, [Service].HoursAtService, [Type].ServiceHours 
FROM 
    [Session] INNER JOIN [Device] ON [Session].Device_uid = [Device].Device_uid 
    [Service] INNER JOIN [Device] ON [Service].Device_uid = [Device].Device_uid
    [Type] INNER JOIN [Device] ON [Type].Type_uid = [Device].Type_uid
WHERE
    [Device].Type_uid = ${my_type_uid} AND [Device].Device_uid = ${my_uid}

将多个SQL SELECT语句组合成一个

3 个答案: