我想减少数量字段并减少其数量

Question

CREATE PROCEDURE dbo.IssueBook
    (
    @bookid nvarchar(50),
    @ano nvarchar(50),
    @mid int,
    @librarian varchar(10),
    @quantity int
    )
AS
    declare @cnt int
    declare @msg varchar(100)
    if  not exists( select * from books where bookid = @bookid and quantity = @quantity) 
       begin
         raiserror('Book is not available',16,1);      
         return;
       end;


    select @cnt = count(bookid) from issues where mid = @mid;
    if ( @cnt >= 2 )   
        begin
         raiserror('Maximum Limit Has Been Reached For Member!',16,1);
         return;
       end;

    begin tran
    begin try 
      update books set quantity =@quantity-1 where bookid= @bookid;
      insert into issues values (@bookid, @mid, getdate(), @librarian, @ano);
      commit tran
    end try
    begin catch
         rollback tran
         /* select  @msg = error_message() */
         raiserror( 'Unknown Error', 16,1);
    end catch

我想更改 sql 表中 quantity 字段的值，我该怎么做，请帮助我，我尝试了很多东西，但它们不起作用，我将非常感谢你...

Answer 1

我认为问题出在这部分：set quantity =@quantity-1。如果我理解正确，它应该是

set quantity = quantity-1 -- Decreease the book quantity by 1

或

set quantity = quantity - @quantity -- Decreease the book quantity by @quantity