Question

如果列不存在，我在使用Alter Table时遇到问题。

这是我的代码：

DECLARE @appId INT
DECLARE @cursor CURSOR

IF NOT EXISTS(SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE COLUMN_NAME = 'MinMktIdeaParticipants' AND TABLE_NAME = 'mkIdeaCategories')
BEGIN
    ALTER TABLE mkIdeaCategories
        ADD MinMktIdeaParticipants int NOT NULL DEFAULT 1
END

IF EXISTS(SELECT Value FROM appConfiguration WHERE CodeId = 16 AND AppConfigurationTypeId = 3 AND ModuleId = 10)
BEGIN
    SET @cursor = CURSOR FAST_FORWARD
    FOR
        SELECT ApplicationId FROM mkMarket
        OPEN @cursor
            FETCH NEXT FROM @cursor INTO @appId
                WHILE (@@Fetch_Status >= 0)
                BEGIN
                    UPDATE 
                        mkIdeaCategories
                    SET MinMktIdeaParticipants = (SELECT Value FROM appConfiguration 
                        WHERE ApplicationId = @appId AND CodeId = 16 AND AppConfigurationTypeId = 3 AND ModuleId = 10)
                    WHERE IdeaCatId IN 
                        (select distinct(theme.IdeaCatId) from dbo.mkIdeaCategories theme
                        inner join dbo.mkMarketIdeaCategories mic ON theme.IdeaCatId = mic.IdeaCatId
                        inner join mkMarket m on m.MarketId=mic.MarketId 
                        WHERE m.ApplicationId = @appId)
                    FETCH NEXT FROM @cursor INTO @appId
                END
        CLOSE @cursor
    DEALLOCATE @cursor
    DELETE * FROM appConfiguration WHERE CodeId = 16 AND AppConfigurationTypeId = 3 AND ModuleId = 10
END

我认为没有任何错误。由于某种原因，输出错误是

Msg 207，Level 16，State 1，Line 53
列名称无效＆＃39; MinMktIdeaParticipants＆＃39;。

我已经搜索过类似的问题，但无法找到解决问题的答案。

Answer 1

当SQL Server处理脚本时，有两个阶段。第一阶段是汇编。第二个是执行。

您收到的错误是编译错误。无论if条件如何，都会编译所有代码。因此，您收到错误，因为该列不存在。在执行阶段之前不会创建该列。

一种解决方案是使用exec（或更好的exec sp_executesql）将代码的第二部分更改为动态SQL，以执行代码。

Answer 2

Gordon Linoff的解决方案将起作用。实现所需的另一种方法是将整个语句包装在存储过程中。

这将失败：

select * from nonexisting_table

这将创建一个存储过程：

create procedure nonsense
as
begin
select * from nonexisting_table
end

但您的查询中存在错误：

SET @cursor = CURSOR FAST_FORWARD

要在sql server中创建快进游标，您必须声明它。这是我最喜欢的mssqltips.com示例：

DECLARE db_cursor CURSOR FAST_FORWARD FOR  
SELECT name 
FROM MASTER.dbo.sysdatabases 
WHERE name NOT IN ('master','model','msdb','tempdb')  

OPEN db_cursor   
FETCH NEXT FROM db_cursor INTO @name   

WHILE @@FETCH_STATUS = 0   
BEGIN   
       SET @fileName = @path + @name + '_' + @fileDate + '.BAK'  
       BACKUP DATABASE @name TO DISK = @fileName  

       FETCH NEXT FROM db_cursor INTO @name   
END   

CLOSE db_cursor   
DEALLOCATE db_cursor

SQL - 在IF NOT EXISTS之后添加列和设置值

2 个答案: