SQL

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
Invalid column name 'MinMktIdeaParticipants'.

我已经搜索过类似的问题，但找不到解决问题的答案。

Answer 1

当SQL 服务器处理脚本时，有两个阶段。第一阶段是编译。二是执行。

您遇到的错误是编译错误。 All 代码被编译，而不管 if 条件。因此，您会收到错误消息，因为该列不存在。直到执行阶段才会创建该列。

一个解决方案是将代码的第二部分更改为动态 SQL，使用 exec（或更好的 exec sp_executesql）来执行代码。

Answer 2

Gordon Linoff 的解决方案会奏效。另一种实现您想要的方法是将整个语句包装在存储过程中。

这会失败：

select * from nonexisting_table

这将创建一个存储过程：

create procedure nonsense
as
begin
select * from nonexisting_table
end

但是您的查询有错误：

SET @cursor = CURSOR FAST_FORWARD

要在 sql 服务器中创建快进游标，您必须声明它。那是我最喜欢的例子 mssqltips.com:

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 后添加列和设置值

SQL - Add column and set value after IF NOT EXISTS

alter-table

sql-server-2008-r2