如何使用 vb.net 和 SQL Server 检查记录是否存在

Question

假设我有两个表Historytable 和studentInformation table。

我想做的是：

If schoolyear and level exist in Historytable
    update studentInformationtable
else
   INSERT schoolyear,level to Historytable
    update studentInformationtable

我的存储过程代码：

ALTER PROCEDURE [dbo].[InsertUpdate] 
    @studentID INT, 
    @SchoolYear Nvarchar(20),
    @levels Nvarchar(20),
    @FirstName Nvarchar(20),
    @SurName Nvarchar(20)
AS
BEGIN
    SET NOCOUNT ON;

BEGIN TRAN
    IF exists (SELECT SchoolYear, Levels
               FROM StudentHistory WITH (updlock, serializable) 
               WHERE StudentID = @studentID)
    BEGIN
        UPDATE StudentInformation
        SET FirstName = @FirstName ,
            Surname = @SurName
        WHERE StudentID = @studentID
    END
    ELSE
    BEGIN
        INSERT INTO Studenthistory (StudentID, SchoolYear, Levels)
        VALUES (@studentID, @SchoolYear, @levels)

        UPDATE StudentInformation
        SET FirstName = @FirstName,
            Surname = @SurName
        WHERE StudentID = @studentID
    END

    COMMIT TRAN
END

vb.net 代码

Using cmd As New SqlClient.SqlCommand("dbo.InsertUpdate", cn)
    cmd.Parameters.AddWithValue("@studentID", frmView.dgv1.SelectedCells(0).Value)
    cmd.CommandType = CommandType.StoredProcedure
    cmd.Parameters.Add("@SurName", SqlDbType.VarChar, 100).Value = txtStudLN.Text
    cmd.Parameters.Add("@FirstName", SqlDbType.VarChar, 100).Value = txtStudFN.Text
    cmd.Parameters.Add("@SchoolYear", SqlDbType.VarChar, 100).Value = cboSchoolYear.Text
    cmd.Parameters.Add("@levels", SqlDbType.VarChar, 100).Value = cboGradeLevel.Text
    cmd.ExecuteNonQuery()
    MsgBox("Update New record successfully")
End Using

问题：当我插入一个新的schoolyear 和level 时，我的历史记录表中没有INSERT 一个新记录。有人可以帮我修复我的代码吗？谢谢

Answer 1

试试这个：

ALTER PROCEDURE [dbo].[InsertUpdate] 
    -- Add the parameters for the stored procedure here

@studentID INT, 
@SchoolYear Nvarchar(20),
@levels Nvarchar(20),
@FirstName Nvarchar(20),
@SurName Nvarchar(20)


AS
BEGIN

    SET NOCOUNT ON;

BEGIN TRAN

   UPDATE StudentInformation
   SET FirstName = @FirstName ,
   Surname = @SurName
   WHERE StudentID = @studentID

   INSERT INTO Studenthistory (StudentID,SchoolYear, Levels)
   SELECT @studentID,@SchoolYear,@levels
   WHERE NOT EXISTS(
        SELECT 1
        FROM Studenthistory
        WHERE StudentID = @studentID
   )


COMMIT TRAN
END

注意事项：

1. 不需要在 if 和 else 部分都写 update 语句。
2. 仅当 select 语句将返回记录时，insert 语句才会将新记录添加到 Studenthistory。 where 子句中的条件确保每个学生只插入一条记录到历史记录表中。

但是，我认为为每个学生只保留一份历史记录没有多大意义。我认为您的意思是要保留每个学生的学年和水平以前的值。如果这是真的，exists 内的查询应该是这样的：

SELECT 1
FROM Studenthistory
WHERE StudentID = @studentID
AND SchoolYear = @SchoolYear,
AND Levels = @levels