我将如何获取最后一个最大记录ID，增量ID，然后将记录添加到表C＃应用程序中

Question

The following code enters a new record into a table. However, for some reason it is picking up 3126 and a record for that ID already exists. Every time I run this function it increments by 1 but there is already a corresponding value for the id until 3198. How would I change and what changes would I make, so that it gets the max value that already exists in the record and increments the ID by 1 and then add the record.

SqlConnection conn = new SqlConnection(Properties.Settings.Default.ConnectionString);
try
{
    conn.Open();

    SqlCommand sqlCMD = new SqlCommand("InsertNewDeal", conn);

    sqlCMD.CommandType = System.Data.CommandType.StoredProcedure;
    sqlCMD.Parameters.Add("@Title", System.Data.SqlDbType.VarChar, 100);
    sqlCMD.Parameters.Add("@Office", System.Data.SqlDbType.Char, 3);
    sqlCMD.Parameters.Add("@EntryBy", System.Data.SqlDbType.VarChar, 50);
    sqlCMD.Parameters.Add("@CSR1", System.Data.SqlDbType.VarChar, 50);
    sqlCMD.Parameters.Add("@id", System.Data.SqlDbType.Int);
    sqlCMD.Parameters["@id"].Direction = System.Data.ParameterDirection.Output;


    sqlCMD.Parameters["@Title"].Value = txtName.Text;
    sqlCMD.Parameters["@Office"].Value = cmbOffice.SelectedValue;
    sqlCMD.Parameters["@CSR1"].Value = cmbCSR.SelectedValue;
    sqlCMD.Parameters["@EntryBy"].Value = LisaDatabaseManager.CurrentCSR.Username;

    CSR user = CSR.LoadCurrentUser();
    sqlCMD.ExecuteNonQuery();
    this.newProductionID = (int)sqlCMD.Parameters["@id"].Value;


    SqlCommand cmd = new SqlCommand("UPDATE Productions SET CountryCode = 'CAN', ProvinceCode = '" + user.GetProvinceCode() + "' WHERE ID = " + newProductionID, conn);
    cmd.ExecuteNonQuery();

    AddOptionalFields(newProductionID);

    LisaDatabaseManager.DealsTable.Fill(LisaDatabaseManager.DSGlobal.LoadDeals);
    DialogResult = DialogResult.OK;
    Close();
}
catch (Exception ex)
{
    ExceptionHandler.LogException("New deal", ex, LogSource.CHECK);
}
finally
{
    conn.Close();
}
}
}

The stored Procedure to InsertNewdeal is the following:

ALTER PROCEDURE [dbo].[InsertNewDeal]
    @Title varchar(100),
    @EntryBy varchar(50),
    @Office char(3),
    @CSR1 varchar(50),
    @id int OUTPUT
AS
BEGIN
    SET NOCOUNT ON;
    declare @CamProb int;
    IF @PSOffice = 'VAN'
        set @CamProb = 1;
    else
        set @CamProb = NULL;

    INSERT INTO Productions(Title, EntryDate, EntryBy, Camera, Light, Grip, Generator, Expendables,IsDead, Office, CSR1, Indie,ProbCam)
        VALUES (@Title, CURRENT_TIMESTAMP, @EntryBy, 0,0,0,0,0,0, @Office, @CSR1,0,@CamProb);

    SELECT @id = Scope_Identity();

    INSERT INTO PostMortems(ProductionID,Indie) VALUES (@id,0);

    INSERT INTO Deals(Production, Date, SubRentals,InsuranceOnFile,DealOnFile, ChargeDVan, Charge5Tonne, ChargeDVan_out, Charge5Tonne_out, ChargeBulbReplacement) VALUES(@id,CURRENT_TIMESTAMP, 'Cost+10%',0,0, 75.00, 100.00, 150.00, 200.00, 1);

    DECLARE ItemCursor Cursor FOR
        select item from dealitems where id in (46048, 46052, 46036, 1, 46054, 15, 46056, 46057, 46058)
        order by
        case
            when id = 46048 then 1
            when id = 46052 then 2
            when id = 46036 then 3
            when id = 1 then 4
            when id = 46054 then 5
            when id = 15 then 6
            when id = 46056 then 7
            when id = 46057 then 8
            else 9
        end

    DECLARE @Description varchar(100)
    DECLARE @count int
    Set @count = 0

    OPEN ItemCursor

    FETCH NEXT FROM ItemCursor INTO @Description

    WHILE @@FETCH_STATUS = 0
    BEGIN
        INSERT INTO DealMemoItems(Deal, Item, Ord)
        VALUES(@id, @Description, @count)

        SET @count = (@count + 1)

        FETCH NEXT FROM ItemCursor INTO @Description
    END
    CLOSE ItemCursor
    DEALLOCATE ItemCursor
END

Answer 1

(SELECT TOP 1 id FROM <yourtable> ORDER BY id DESC) + 1

This gets the last highest ID from the table, and increments it by one. You can put it right into your SQL insert statement, as a value, like below:

INSERT INTO <YOURTABLE> (id, name)
values (
     (SELECT TOP 1 id FROM <yourtable> ORDER BY id DESC) + 1,
     'Goober fish'
);

Answer 2

Could you not change your stored procedure to use:

SELECT SCOPE_IDENTITY()

Which would return the id of the last inserted record. You cannot rely on the id being equal to the largest id incremented by one, as ids can be reused overtime.

Note this is a SQL Server solution, but there are usually equivalents in other database engines.