问题描述
来自这个答案:有没有办法在不使用游标的情况下遍历 TSQL 中的表变量?
我正在使用该方法
WHILE EXISTS(SELECT * FROM #Temp)
问题是它输出了多个表，如果可能的话，我想输出为一个表.
The problem is that it's outputting multiple tables, if possible I'd like to output as a single table.
Declare @Id int
WHILE EXISTS(SELECT * FROM #Temp)
Begin
Select Top 1 @Id = Id From #Temp
--Do some processing here
Delete #Temp Where Id = @Id
End
所以现在它输出这个:
x y
-- --
1 a
x y
-- --
1 b
但我希望它输出这个:
x y
-- --
1 a
2 b
我正在努力实现的目标，我在一个领域有这个目标:
What I'm trying to achieve, I have this in a field:
1234,1432,1235
1234,1432,1235
我有一个将字段拆分为记录的过程(它适用于 sql server 2000):
I have a process that splits the field into records(it works with sql server 2000):
DECLARE @String VARCHAR(100)
SELECT @String = str FROM field --with the 1234,1432,1235
SELECT SUBSTRING(',' + @String + ',', Number + 1,
CHARINDEX(',', ',' + @String + ',', Number + 1) - Number -1)AS str
INTO #temp
FROM master..spt_values
WHERE Type = 'P'
AND Number <= LEN(',' + @String + ',') - 1
AND SUBSTRING(',' + @String + ',', Number, 1) = ','
GO
所以现在，#temp 有:
So now, #temp has:
str
---
1234
1432
1235
所以我需要遍历每条记录来查询我需要的信息.
So I need to go through each record to query the information I need.
我希望它输出如下内容:
And I'd like it to output something like this:
str name age
--- ---- ---
1234 Bob 23
1432 Jay 41
1235 Tim 12
当前的 While 循环输出如下，我不想要:
The current While loop outputs it like this, which I don't want:
str name age
--- ---- ---
1234 Bob 23
str name age
--- ---- ---
1432 Jay 41
str name age
--- ---- ---
1235 Tim 12
最终工作结果:
SET NOCOUNT ON;
DECLARE @String VARCHAR(1000);
SELECT @String = Tnn FROM (SELECT
CO.USER_2 AS Tnn
FROM
[VMFG].[dbo].[CUSTOMER_ORDER] AS CO
LEFT JOIN DBO.Tnn_Header AS Tnn ON Tnn.TnnNumber = CO.USER_2 AND Tnn.StatusID = '5' WHERE CO.ID = 'ORDERID') AS Place --with the 1234,1432,1235
DECLARE @Id nvarchar(50),
@Discount nvarchar(50),
@Spin nvarchar(50),
@Commission_Hmm nvarchar(50),
@Commission nvarchar(50),
@TnnID nvarchar(50);
DECLARE @Output TABLE (
TnnNumber nvarchar(50),
Discount nvarchar(50),
Spin nvarchar(50),
Commission_Hmm nvarchar(50),
Commission nvarchar(50),
TnnID nvarchar(50));
DECLARE crs CURSOR STATIC LOCAL READ_ONLY FORWARD_ONLY
FOR SELECT SUBSTRING(',' + @String + ',', Number + 1,
CHARINDEX(',', ',' + @String + ',', Number + 1) - Number -1) AS [ID]
FROM master..spt_values
WHERE Type = 'P'
AND Number <= LEN(',' + @String + ',') - 1
AND SUBSTRING(',' + @String + ',', Number, 1) = ',';
OPEN crs;
FETCH NEXT
FROM crs
INTO @Id;
WHILE (@@FETCH_STATUS = 0)
BEGIN
-- do some processing..
SELECT
@Id = TH.TnnNumber,
@Discount = CASE WHEN COUNT(DISTINCT TL.DiscountCodeID) > 1 THEN 'Varies, View Tnn' ELSE CAST(MAX(DC.Value) AS VARCHAR(60)) END,
@Spin = CASE WHEN TS.SpinID > 4 THEN 'Has Specifics, View Tnn' ELSE TS.Value END,
@Commission_Hmm = CASE WHEN COUNT(DISTINCT TL.Commission_Hmm) > 1 THEN 'Varies, View Tnn' ELSE CAST(MAX( ISNULL(str(TL.Commission_Hmm,12),'Default Comm')) AS VARCHAR(60)) END,
@Commission = CASE WHEN COUNT(DISTINCT TL.Commission) > 1 THEN 'Varies, View Tnn' ELSE CAST(MAX(ISNULL(str(TL.Commission,12),'Default Comm')) AS VARCHAR(60)) END,
@TnnID = TL.TnnID
FROM DBO.Tnn_Header AS TH
LEFT JOIN DBO.Tnn_LINE AS TL ON TH.TnnID = TL.TnnID
LEFT JOIN DBO.Tnn_Spin AS TS ON TH.SpinID = TS.SpinID
LEFT JOIN DBO.Tnn_DiscountCode AS DC ON TL.DiscountCodeID = DC.DiscountCodeID
WHERE TnnNumber = @id
GROUP BY
TH.TnnNumber,
TS.SpinID,
TS.Value,
TL.TnnID
-- end do some processing..
INSERT INTO @Output (TnnNumber, Discount, Spin, Commission_Hmm, Commission, TnnID)
VALUES (@Id, @Discount, @Spin, @Commission_Hmm, @Commission, @TnnID);
FETCH NEXT
FROM crs
INTO @Id;
END;
CLOSE crs;
DEALLOCATE crs;
SELECT TnnNumber, Discount, Spin, Commission_Hmm, Commission, TnnID
FROM @Output;
推荐答案
遵循这些糟糕的建议是在浪费时间和精力.如果您绝对必须(特别强调必须)采用逐行方法(CURSOR 或 WHILE 循环)，那么最好使用 CURSOR.它是一种更高效且不易出错的内置结构.您只需要使用正确的选项，例如使其成为 STATIC、LOCAL、READ_ONLY 和 FORWARD_ONLY.如果游标查询仅命中临时表和/或表变量，则不需要 STATIC.
You are wasting your time and energy following such bad advice. If you absolutely must (extra emphasis on the must) take a row-by-row approach (CURSOR or WHILE loop), then you are better off with a CURSOR. It is a built-in construct that is more efficient, and less error-prone. You just need to use the right options, such as making it STATIC, LOCAL, READ_ONLY, and FORWARD_ONLY. You don't need STATIC if the cursor query is only hitting temporary tables and/or table variables.
人们会对此争论不休，并说您必须不惜一切代价避免使用游标！"，但他们还没有进行测试以证明这种流行的概念实际上只是一个神话.如果他们已经进行了似乎证实了这一点的测试，那么他们还没有设置适当的选项，主要是 STATIC，它将游标查询的结果转储到临时表中.如果没有这个选项，获取新行将重新检查基表以确保它们仍然存在，并且那就是性能下降的地方(I/O 加上锁定).这也是为什么在仅查询临时表和/或表变量时通常不需要 STATIC 选项的原因.我所说的重新检查"是什么意思?只需查看 @@FETCH_STATUS 的文档即可.返回值不仅仅包括成功"(0)和没有更多行"(-1):还有一个返回值，(-2)，意思是获取的行丢失".
People will argue with this and say that "you must avoid cursors at all cost!", but they haven't done the tests to see that such a popular notion is really just a myth. And if they have done tests that appear to confirm it, then they haven't set the appropriate options, mostly STATIC, which dumps the result of the cursor query into a temp table. Without this option, fetching new rows will re-check the base tables to make sure that they still exist, and that is where the performance hit is (the I/O plus the locking). And that is also why you typically don't need the STATIC option when querying only temporary tables and/or table variables. What do I mean by "re-checking"? Just look at the documentation for @@FETCH_STATUS. The return values don't just cover "success" (0) and "no more rows" (-1): there is a return value, (-2), that means "The row fetched is missing".
SET NOCOUNT ON;
DECLARE @Id INT,
@Name sysname,
@Type VARCHAR(5);
-- the Table Variable replaces #Temp2 in the original query
DECLARE @Output TABLE (Id INT NOT NULL, Name sysname, [Type] VARCHAR(5));
-- the CURSOR replaces #Temp in the original query
DECLARE crs CURSOR STATIC LOCAL READ_ONLY FORWARD_ONLY
FOR SELECT [object_id], name, [type]
FROM sys.objects -- dbo.sysobjects for SQL 2000 -- ATable in the original query
ORDER BY [object_id] ASC;
OPEN crs;
FETCH NEXT
FROM crs
INTO @Id, @Name, @Type;
WHILE (@@FETCH_STATUS = 0)
BEGIN
INSERT INTO @Output (Id, Name, [Type])
VALUES (@Id, @Name, @Type);
-- do some processing..
FETCH NEXT -- replaces the DELETE and re-SELECT in the original query
FROM crs
INTO @Id, @Name, @Type;
END;
CLOSE crs;
DEALLOCATE crs;
SELECT Id, Name, [Type]
FROM @Output;
更新
假设迭代是在一个拆分 INT 的 CSV 的查询上完成的，结果查询将类似于以下内容:
Given the iteration is being done over a query that splits a CSV of INTs, the resulting query would look similar to the following:
SET NOCOUNT ON;
DECLARE @String VARCHAR(1000);
SELECT @String = str FROM [Table]; --with the 1234,1432,1235
DECLARE @Id INT,
@Name NVARCHAR(50),
@Age TINYINT;
DECLARE @Output TABLE (Id INT NOT NULL, Name NVARCHAR(50), Age TINYINT);
DECLARE crs CURSOR STATIC LOCAL READ_ONLY FORWARD_ONLY
FOR SELECT SUBSTRING(',' + @String + ',', Number + 1,
CHARINDEX(',', ',' + @String + ',', Number + 1) - Number -1) AS [ID]
FROM master..spt_values
WHERE Type = 'P'
AND Number <= LEN(',' + @String + ',') - 1
AND SUBSTRING(',' + @String + ',', Number, 1) = ',';
OPEN crs;
FETCH NEXT
FROM crs
INTO @Id;
WHILE (@@FETCH_STATUS = 0)
BEGIN
-- do some processing..
-- Logic to set value of @Name
-- Logic to set value of @Age
INSERT INTO @Output (Id, Name, Age)
VALUES (@Id, @Name, @Age);
FETCH NEXT
FROM crs
INTO @Id;
END;
CLOSE crs;
DEALLOCATE crs;
SELECT Id, Name, Age
FROM @Output;
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