SQL 服务器 - 如何创建 IF EXISTS...SELECT AND SELECT

Question

我正在尝试对我的代码创建一个 IF/ELSE 检查，以确保参数 @BookTitle 和 @GenreName 是表 BookGenre 和尝试删除它们之前的流派。我试图编写这行代码，但收到错误，

An expression of type non-Boolean type specified where condition is expected.

IF EXISTS (SELECT Id FROM Library.Book WHERE Title = @BookTitle AND 
               SELECT Id FROM Library.Genre WHERE Name = @GenreName)
ELSE

我需要一些指导，了解如何创建包含两个单独的 select 语句的 IF EXISTS 语句表达式作为 IF 检查的一部分。

下面是完整的存储过程（没有 IF 语句）：

PROCEDURE [Library].[DeleteDateFromBookGenre]
        -- Parameters to select which record delete
        @BookTitle nvarchar(200),
        @GenreName nvarchar(50)
    AS
    BEGIN
        -- SET NOCOUNT ON added to prevent extra result sets from
        -- interfering with SELECT statements.
        SET NOCOUNT ON;

        IF EXISTS (SELECT Id FROM Library.Book WHERE Title = @BookTitle) 
        IF EXISTS (SELECT Id FROM Library.Book WHERE Title = @BookTitle)

        -- Deletes the specified and selected data from the Genre and Book table.
        DELETE FROM Library.BookGenre 
        WHERE BookId IN (
        SELECT Id
        FROM Library.Book
        WHERE Title = @BookTitle
        ) AND
        GenreId IN (
        SELECT Id
        FROM Library.Genre
        WHERE Name = @GenreName
        )
    END

Answer 1

你的括号不对；你需要两个 EXISTS 条件：

IF EXISTS (SELECT Id FROM Library.Book WHERE Title = @BookTitle
          ) AND 
   EXISTS (SELECT Id FROM Library.Genre WHERE Name = @GenreName
          )
BEGIN
    . . .
END

SQL 服务器 - 如何创建 IF EXISTS...SELECT AND SELECT

SQL Server - How to create IF EXISTS...SELECT AND SELECT

sql

sql-server

tsql

dml