Question

我知道游标是不受欢迎的，我尽量避免使用它们，但可能有一些合理的理由使用它们。我有一个，我试图使用一对游标：一个用于主表，一个用于辅助表。主表游标在外部循环中遍历主表。辅助表游标迭代内部循环中的辅助表。问题是，主表游标虽然显然正在进行并将主键列值[Fname]保存到本地变量@Fname中，但它没有获得辅助表中相应外键列的行。对于辅助表，它始终返回其外键列值与主表的第一行的主键列值匹配的行。

以下是我想在实际存储过程中做的非常简化的示例。名称是主表

SET NOCOUNT ON
DECLARE 
    @Fname varchar(50) -- to hold the fname column value from outer cursor loop
    ,@FK_Fname varchar(50) -- to hold the fname column value from inner cursor loop
    ,@score int
;

--prepare primary table to be iterated in the  outer loop
DECLARE @Names AS Table (Fname varchar(50))
INSERT @Names
    SELECT 'Jim' UNION
    SELECT 'Bob' UNION
    SELECT 'Sam' UNION
    SELECT 'Jo' 


--prepare secondary/detail table to be iterated in the inner loop
DECLARE @Scores AS Table (Fname varchar(50), Score int)
INSERT @Scores
    SELECT 'Jo',1 UNION
    SELECT 'Jo',5 UNION
    SELECT 'Jim',4 UNION
    SELECT 'Bob',10 UNION
    SELECT 'Bob',15 

--cursor to iterate on the primary table in the outer loop
DECLARE curNames CURSOR
FOR SELECT Fname FROM @Names


OPEN curNames
FETCH NEXT FROM curNames INTO @Fname

--cursor to iterate on the secondary table in the inner loop
DECLARE curScores CURSOR
FOR 
    SELECT FName,Score 
    FROM @Scores 
    WHERE Fname = @Fname 
 --*** NOTE: Using the primary table's column value @Fname from the outer loop

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT 'Outer loop @Fname = ' + @Fname

    OPEN curScores
    FETCH NEXT FROM curScores INTO @FK_Fname, @Score

    WHILE @@FETCH_STATUS = 0
    BEGIN
        PRINT ' FK_Fname=' + @FK_Fname + '. Score=' + STR(@Score)
        FETCH NEXT FROM curScores INTO @FK_Fname, @Score
    END
    CLOSE curScores
    FETCH NEXT FROM curNames INTO @Fname
END

DEALLOCATE curScores

CLOSE curNames
DEALLOCATE curNames

这是我得到的结果。请注意，对于外部循环，它会显示最新的Fname，但是当该Fname用作@Fname以从次表中获取相关行以进行后续迭代时，它仍会获得与第一个匹配的行主表的行（Bob）。

Outer loop @Fname = Bob
    FK_Fname=Bob. Score=10
    FK_Fname=Bob. Score=15
Outer loop @Fname = Jim
    FK_Fname=Bob. Score=10
    FK_Fname=Bob. Score=15
Outer loop @Fname = Jo
    FK_Fname=Bob. Score=10
    FK_Fname=Bob. Score=15
Outer loop @Fname = Sam
    FK_Fname=Bob. Score=10
    FK_Fname=Bob. Score=15

请让我知道我做错了什么。提前谢谢！

Answer 1

@fName的值在以下位置计算：DECLARE curScores CURSOR，而不是在主循环中。您必须声明然后在主循环中取消分配secon光标。

Answer 2

由于提示很少，我找到了解决方案。

我必须在第一个循环内DECLARE和DEALLOCATE辅助光标。我最初讨厌这样做，因为我认为在循环中放置和释放资源并不是一个好主意，但我认为在这种特定情况下没有其他方法可以避免这种情况。 Noew工作代码看起来像这样：

SET NOCOUNT ON
DECLARE 
    @Fname varchar(50) -- to hold the fname column value from outer cursor loop
    ,@FK_Fname varchar(50) -- to hold the fname column value from inner cursor loop
    ,@score int
;

--prepare primary table to be iterated in the  outer loop
DECLARE @Names AS Table (Fname varchar(50))
INSERT @Names
    SELECT 'Jim' UNION
    SELECT 'Bob' UNION
    SELECT 'Sam' UNION
    SELECT 'Jo' 


--prepare secondary/detail table to be iterated in the inner loop
DECLARE @Scores AS Table (Fname varchar(50), Score int)
INSERT @Scores
    SELECT 'Jo',1 UNION
    SELECT 'Jo',5 UNION
    SELECT 'Jim',4 UNION
    SELECT 'Bob',10 UNION
    SELECT 'Bob',15 

--cursor to iterate on the primary table in the outer loop
DECLARE curNames CURSOR
FOR SELECT Fname FROM @Names


OPEN curNames
FETCH NEXT FROM curNames INTO @Fname

--cursor to iterate on the secondary table in the inner loop
DECLARE curScores CURSOR
FOR 
    SELECT FName,Score 
    FROM @Scores 
    WHERE Fname = @Fname 
 --*** NOTE: Using the primary table's column value @Fname from the outer loop

WHILE @@FETCH_STATUS = 0
BEGIN
    PRINT 'Outer loop @Fname = ' + @Fname

    OPEN curScores
    FETCH NEXT FROM curScores INTO @FK_Fname, @Score

    WHILE @@FETCH_STATUS = 0
    BEGIN
        PRINT ' FK_Fname=' + @FK_Fname + '. Score=' + STR(@Score)
        FETCH NEXT FROM curScores INTO @FK_Fname, @Score
    END
    CLOSE curScores
    FETCH NEXT FROM curNames INTO @Fname
END

DEALLOCATE curScores

CLOSE curNames
DEALLOCATE curNames

我得到了正确的结果：

Outer loop @Fname = Bob
    FK_Fname=Bob. Score=        10
    FK_Fname=Bob. Score=        15
Outer loop @Fname = Jim
    FK_Fname=Jim. Score=         4
Outer loop @Fname = Jo
    FK_Fname=Jo. Score=         1
    FK_Fname=Jo. Score=         5
Outer loop @Fname = Sam

Answer 3

我认为使用具有行号的临时表可以更轻松地完成此操作：

create table #temp1
(
 row int identity(1,1)
 , ... 
)

看起来你真的要求SQL表现得像一个喜欢循环的语言。它没有。每当我发现自己在SQL中编写循环时，我会问自己，是否必须以这种方式完成？ 7/10的答案是否定的，我可以用套装来做。

Answer 4

我会尝试放置

DECLARE curScores CURSOR
FOR 
    SELECT FName,Score 
    FROM @Scores 
    WHERE Fname = @Fname

在第一个内部，因为您只声明游标的第一个名称值

T-Sql游标不在fetch上继续

4 个答案: