使用sql中的子查询从另一个表中计算id

Question

我想按照指定的批次统计学生的id。学生 ID 位于其他表中。我正在尝试从 dbo.Batches 中获取所有批次的详细信息，其中包含批处理 ID。同时我想计算那批注册的学生人数。 studentid 和批次 id 位于 dbo.studentbatchrelation 表中。到目前为止，我尝试过的是，应用子查询来生成批次的详细信息以及在特定批次中注册的学生人数。

以下是我的查询：

查询

(Select 
     Count(studentId) as TotalStudents 
 from 
     dbo.StudentBatchRelation 
 where 
     BatchId in (Select 
                     b.Id as BatchId, b.CourseId as CourseId, 
                     b.BatchNumber as BatchNumber,
                     b.BatchTimingsFrom as BatchTimingsFrom, 
                     b.BatchTimingsTo as BatchTimingsTo, 
                     b.BatchDuration as Duration, b.BatchDate as BatchDate,
                     b."Days" as "Days", b.CourseRoomId as CourseRoomId,  
                     c.CourseName as CourseName, 
                     cr.RoomName as RoomName, 
                     cr.RoomCapacity as RoomCapacity 
                 from 
                     dbo."Batches" b, dbo.Courses c,
                     dbo.CourseRooms cr 
                 where 
                     b.CourseId = c.Id 
                     and b.CourseRoomId = cr.Id 
                     and b.ActiveBatch = 1  ));

批次的表结构

CREATE TABLE [dbo].[Batches] (
    [Id]               VARCHAR (250) NOT NULL,
    [CourseId]         VARCHAR (250) NOT NULL,
    [BatchNumber]      VARCHAR (250) NOT NULL,
    [BatchTimingsFrom] TIME (7)      NOT NULL,
    [BatchTimingsTo]   TIME (7)      NOT NULL,
    [BatchDuration]    VARCHAR (50)  NOT NULL,
    [Days]             VARCHAR (250) NOT NULL,
    [CourseRoomId]     VARCHAR (250) NOT NULL,
    [BatchDate]        VARCHAR (250) NULL,
    [ActiveBatch]      BIT           DEFAULT ((0)) NULL,
    CONSTRAINT [PK_Batches] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_BATCHES_COURSE] FOREIGN KEY ([CourseId]) REFERENCES [dbo].[Courses] ([Id]) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT [FK_BATCHES_CourseRoom] FOREIGN KEY ([CourseRoomId]) REFERENCES [dbo].[CourseRooms] ([Id]) ON DELETE CASCADE ON UPDATE CASCADE
);

StudentBatchRelation 的表结构

CREATE TABLE [dbo].[StudentBatchRelation] (
    [Id]              VARCHAR (250) NOT NULL,
    [BatchId]         VARCHAR (250) NOT NULL,
    [StudentId]       VARCHAR (250) NOT NULL,
    [TransactionId]   VARCHAR (250) NULL,
    [RemainingAmount] VARCHAR (250) NULL,
    [Status]          VARCHAR (250) NULL,
    CONSTRAINT [PK_StudentBatchRelation] PRIMARY KEY CLUSTERED ([Id] ASC),
    CONSTRAINT [FK_StudentBatchRelation_Batch] FOREIGN KEY ([BatchId]) REFERENCES [dbo].[Batches] ([Id]) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT [FK_StudentBatch_TransactionId] FOREIGN KEY ([TransactionId]) REFERENCES [dbo].[TransactionTable] ([Id]) ON DELETE CASCADE ON UPDATE CASCADE,
    CONSTRAINT [FK_StudentBatchRelation_Student] FOREIGN KEY ([StudentId]) REFERENCES [dbo].[User] ([Id])
);

Answer 1

我可以更好地使用join；

Select 
     SBR.BatchId, Count(SBR.StudentId) as TotalStudents 
 from 
     dbo.StudentBatchRelation SBR 
     inner join Batches B ON SBR.BatchId = B.Id
     inner join Courses C ON C.Id = B.CourseId
     inner join CourseRooms CR ON CR.Id = B.CourseRoomId
     where B.ActiveBatch = 1
     group by SBR.BatchId

Answer 2

Select 
    b.Id as BatchId, b.CourseId as CourseId, 
    b.BatchNumber as BatchNumber,
    b.BatchTimingsFrom as BatchTimingsFrom, 
    b.BatchTimingsTo as BatchTimingsTo, 
    b.BatchDuration as Duration, b.BatchDate as BatchDate,
    b."Days" as "Days", b.CourseRoomId as CourseRoomId,  
    c.CourseName as CourseName, 
    cr.RoomName as RoomName, 
    cr.RoomCapacity as RoomCapacity 
    ,COUNT(*) OVER (PARTITION BY b.Id) countstudentinBatches
from 
dbo."Batches" b 
INNER JOIN dbo.Courses c ON b.CourseId = c.Id  
INNER JOIN dbo.CourseRooms cr ON b.CourseRoomId = cr.Id 
INNER JOIN dbo.StudentBatchRelation sr ON sr.BatchId = b.Id
WHERE b.ActiveBatch = 1