使用sql中的子查询从另一个表计数id

Question

我想根据指定的批次计算学生的ID。学生ID位于其他表中。我正在尝试的是从包含batchid的dbo.Batches中获取所有批次的详细信息。与此同时，我想计算在该批次中注册的学生人数。 studentid和批处理ID在dbo.studentbatchrelation表中。我到目前为止所尝试的是，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数量。

以下是我的查询：

询问

(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