在迭代中正确使用 @declare 时遇到问题

Question

我发布了另一个问题here

但事实证明，我的问题的第一个解决方案更简单，而且我将设置我的计数设置为在错误的位置进行迭代。 真正的问题是，当我尝试迭代时，我构建数据库名称的值是错误的。

这是 Stack Overflow 上一位友好人士更正的代码，他们通知我发布第二个问题，以用不正确的声明格式澄清这个问题。

主要问题涉及这一行 [EDDS'+cast(@databasename as nvarchar(128))+'].[EDDSDBO].[Document]

--check if the #databases table is already present and then drop it
IF OBJECT_ID('tempdb..#databases', 'U') IS NOT NULL
    drop table #databases;


--create the temp table as outside the loop
create table #databases(
    ID INT IDENTITY,
    ArtifactID VARCHAR(20) -- not sure of this ID's data type
)


--check if your temp table exists and drop if necessary
IF OBJECT_ID('tempdb..#temptable', 'U') IS NOT NULL
    drop table #temptable;

--create the temp table as outside the loop
create table #temptable(
    fileSize dec,
    extractedTextSize dec
)

--this will allow the population of each database name
DECLARE @databasename sysname = '' 

-- initialze to 1 so it matches first record in temp table
DECLARE @LoopOn int = 1; 

--this will be the max  count from table
DECLARE @MaxCount int = 0; 

--Once this first statement has been run there will now be a number column 
that is associated with the artificatID. Each database has an area that is 
--      titled [EDDS'artifactID']. So if the artifactID = 1111111 then the 
DB would be accessed at [EDDS1111111]

-- do insert here so it adds the ID column
INSERT INTO #databases(
    ArtifactID
)
SELECT ArtifactID 
FROM edds.eddsdbo.[Case]
where name like '%Review%'

-- sets the max number of loops we are going to do
select @MaxCount = COUNT(*) 
FROM #databases;

while @LoopOn <= @MaxCount
    BEGIN
        -- your table has IDENTITY so select the one for the loop your on 
(initalize to 1)
        select @databasename = ArtifactID 
        FROM #databases
        WHERE ID = @LoopOn;

        --generate your sql using the @databasename variable, if you want 
to make 
        --the database and table names dynamic too then you can use the 
same formula

        insert into #temptable
        select SUM(fileSize)/1024/1024/1024, 
SUM(extractedTextSize)/1024/1024
        -- dont know/think this will work like this?  If not you have to 
use dynamic SQL 
        FROM [EDDS'+cast(@databasename as nvarchar(128))+'].[EDDSDBO]. 
[Document] ed
    where ed.CreatedDate >= (select CONVERT(varchar,dateadd(d,- (day(getdate())),getdate()),106))

    -- remove all deletes/etc and just add one to the @LoopOn and it will be selected above based off the ID
    select @LoopOn += 1
end

-- Query the final values in the temp table after the iteration is complete
select filesize+extractedTextSize as Gigs 
FROM #temptable

我收到一个错误

无效的对象名称'EDDS'+cast(@databasename as nvarchar(128))+'.EDDSDBO.Document'

如果我手动输入EDDS1111111.EDDSDBO.Document，它可以正常工作。

如果我设置 declare @databasename nvarchar(128) = 1111111 它也会破坏代码。 我认为该错误与我如何将其转换或将其添加到语句中有关。

感谢您提供的任何帮助

Answer 1

您不能像上面那样构建 SQL 并执行，否则会出现您看到的错误，您需要使整个语句动态化。以下是 2 种不同的解决方案，具体取决于大小/复杂性（以防您未发布完整代码）。

这将解决您的问题并为表中的每一行创建动态 SQL。

我将其更新为有 2 个解决方案，一个用于执行动态 SQL 的行数不多，另一个用于处理复杂或大量运行的情况。

第二种解决方案可以针对您的特定场景使用更少的代码进行精简，但按照我下面的方式进行操作，只需更改您插入的 SQL 和临时表以获得结果，您就可以将其用于更多场景.

我自己用一些基本的 sql 表对此进行了测试，两个版本都运行良好。 虽然我没有像您那样进行计算，但取决于您表中的数据，您的计算和/或您的实际选择可能需要更新，因为我无权访问您的实际数据/表进行测试。

我还有几行测试，你显然可以把它们拿出来。

-- this is used to add line breaks to make code easier to read
DECLARE @NewLine AS NVARCHAR(MAX) = CHAR(10)

-- to hold your dynamic SQL for all rows/inserts at once
DECLARE @sql NVARCHAR(MAX) = N'';

-- create temp table to insert your dynamic SQL results into 
IF OBJECT_ID('tempdb..#DatabaseSizes', 'U') IS NOT NULL
    DROP TABLE #DatabaseSizes;

create table #DatabaseSizes(
    fileSize DECIMAL,
    extractedTextSize DECIMAL
)

SELECT @sql = @sql + N'' + 
    'select SUM(fileSize)/1024/1024/1024 as fileSize, SUM(extractedTextSize)/1024/1024 as extractedTextSize ' + @NewLine +          
    'FROM [EDDS' + CAST(ArtifactID as nvarchar(128)) + '].[EDDSDBO].[Document] ed ' + @NewLine +
    'where ed.CreatedDate >= (select CONVERT(varchar,dateadd(d,- (day(getdate())),getdate()),106)) ; ' + @NewLine + @NewLine
FROM edds.eddsdbo.[Case]
WHERE name like '%Review%'


-- for testing/validating 
PRINT @sql

INSERT INTO #DatabaseSizes (
    fileSize,
    extractedTextSize
)
-- executes all the dynamic SQL we just generated
EXEC sys.sp_executesql @SQL;


SELECT * 
FROM #DatabaseSizes


-- &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
-- for solution with a LOT of records from your table that is too large or complex to execute all at once using the above 
-- this will generate seperate dynamic SQL for each row in your table
-- &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&


DECLARE @NewLine AS NVARCHAR(MAX) = CHAR(10)
DECLARE @IdOnFromLoop INT
DECLARE @DynamicSQLFromLoop NVARCHAR(MAX)

-- table to insert data into that our dynamic SQL creates
IF OBJECT_ID('tempdb..#DatabaseSizes', 'U') IS NOT NULL
    DROP TABLE #DatabaseSizes;

create table #DatabaseSizes(
    fileSize DECIMAL,
    extractedTextSize DECIMAL
)

-- this is to hold each rows dynamic SQL so we can loop through them and execute each statement one at a time
IF OBJECT_ID('tempdb..#DynamicSQLPerLoop', 'U') IS NOT NULL
    DROP TABLE #DynamicSQLPerLoop;

create table #DynamicSQLPerLoop(
    ID INT IDENTITY,
    DynamicSQL NVARCHAR(MAX)
)

-- here we build our our dynamic SQL we want for each row in the table to be executed
INSERT INTO #DynamicSQLPerLoop (
    DynamicSQL
)
SELECT 'select SUM(fileSize)/1024/1024/1024 as fileSize, SUM(extractedTextSize)/1024/1024 as extractedTextSize ' + @NewLine +           
    'FROM [EDDS' + CAST(ArtifactID as nvarchar(128)) + '].[EDDSDBO].[Document] ed ' + @NewLine +
    'where ed.CreatedDate >= (select CONVERT(varchar,dateadd(d,- (day(getdate())),getdate()),106)) ; ' + @NewLine + @NewLine
FROM edds.eddsdbo.[Case]
WHERE name like '%Review%'



-- for testing/validating all the rows
SELECT * FROM #DynamicSQLPerLoop

-- need to initalize ID to start on, could default to 1, but if no recordsd found would try to do loop and error out
SELECT @IdOnFromLoop = MIN(ID) 
FROM #DynamicSQLPerLoop

-- now we just loop through all the records, until no more are found
WHILE @IdOnFromLoop IS NOT NULL
    BEGIN
        -- need to get dynamic SQL statement to execute for the loop we are on now
        SELECT @DynamicSQLFromLoop = DynamicSQL
        FROM #DynamicSQLPerLoop
        WHERE ID = @IdOnFromLoop

        -- now we insert the data into our table by executing the dynamic SQL 
        INSERT INTO #DatabaseSizes (
            fileSize,
            extractedTextSize
        )       
        EXEC sys.sp_executesql @DynamicSQLFromLoop


        -- now we get the ID that is one higher than the one we just did, and if none found will exit loop
        SELECT @IdOnFromLoop = MIN(ID) 
        FROM #DynamicSQLPerLoop
        WHERE ID > @IdOnFromLoop

    END -- end looping


SELECT * 
FROM #DatabaseSizes