T-SQL:循环遍历已知值的数组

Question

这是我的情景:

假设我有一个存储过程,我需要在一组特定的id上调用另一个存储过程; 有没有办法做到这一点？

即而不是需要这样做:

exec p_MyInnerProcedure 4
exec p_MyInnerProcedure 7
exec p_MyInnerProcedure 12
exec p_MyInnerProcedure 22
exec p_MyInnerProcedure 19

做这样的事情:

*magic where I specify my list contains 4,7,12,22,19*

DECLARE my_cursor CURSOR FAST_FORWARD FOR
*magic select*

OPEN my_cursor 
FETCH NEXT FROM my_cursor INTO @MyId
WHILE @@FETCH_STATUS = 0
BEGIN

exec p_MyInnerProcedure @MyId

FETCH NEXT FROM my_cursor INTO @MyId
END

我的主要目标是简单的可维护性(随着业务的变化,很容易删除/添加id),能够在一行中列出所有Id ...性能不应该是一个大问题

Answer 1

declare @ids table(idx int identity(1,1), id int)

insert into @ids (id)
    select 4 union
    select 7 union
    select 12 union
    select 22 union
    select 19

declare @i int
declare @cnt int

select @i = min(idx) - 1, @cnt = max(idx) from @ids

while @i < @cnt
begin
     select @i = @i + 1

     declare @id = select id from @ids where idx = @i

     exec p_MyInnerProcedure @id
end

Answer 2

我在这种情况下做的是创建一个表变量来保存ID.

  Declare @Ids Table (id integer primary Key not null)
  Insert @Ids(id) values (4),(7),(12),(22),(19)

- (或调用另一个表值函数来生成此表)

然后根据此表中的行循环

  Declare @Id Integer
  While exists (Select * From @Ids)
    Begin
      Select @Id = Min(id) from @Ids
      exec p_MyInnerProcedure @Id 
      Delete from @Ids Where id = @Id
    End

要么...

  Declare @Id Integer = 0 -- assuming all Ids are > 0
  While exists (Select * From @Ids
                where id > @Id)
    Begin
      Select @Id = Min(id) 
      from @Ids Where id > @Id
      exec p_MyInnerProcedure @Id 
    End

上述方法中的任何一种都比游标快得多(对常规用户表声明).表值变量具有错误的rep,因为当使用不当时(对于具有大量行的非常宽的表),它们不具有高性能.但是如果你只使用它们来保存键值或4字节整数,并带有索引(如本例所示)它们非常快.

Answer 3

使用静态游标变量和拆分函数:

declare @comma_delimited_list varchar(4000)
set @comma_delimited_list = '4,7,12,22,19'

declare @cursor cursor
set @cursor = cursor static for 
  select convert(int, Value) as Id from dbo.Split(@comma_delimited_list) a

declare @id int
open @cursor
while 1=1 begin
  fetch next from @cursor into @id
  if @@fetch_status <> 0 break
  ....do something....
end
-- not strictly necessary w/ cursor variables since they will go out of scope like a normal var
close @cursor
deallocate @cursor

游标具有错误的rep,因为在针对用户表声明时,默认选项会产生大量开销.

但在这种情况下,开销很小,比这里的任何其他方法都少.STATIC告诉SQL Server在tempdb中实现结果,然后迭代它.对于像这样的小型列表,它是最佳解决方案.

Answer 4

我通常使用以下方法

DECLARE @calls TABLE (
    id INT IDENTITY(1,1)
    ,parameter INT
    )

INSERT INTO @calls
select parameter from some_table where some_condition -- here you populate your parameters

declare @i int
declare @n int
declare @myId int
select @i = min(id), @n = max(id) from @calls
while @i <= @n
begin
    select 
        @myId = parameter
    from 
        @calls
    where id = @i

        EXECUTE p_MyInnerProcedure @myId
    set @i = @i+1
end

Answer 5

您可以尝试如下操作：

declare @list varchar(MAX), @i int
select @i=0, @list ='4,7,12,22,19,'

while( @i < LEN(@list))
begin
    declare @item varchar(MAX)
    SELECT  @item = SUBSTRING(@list,  @i,CHARINDEX(',',@list,@i)-@i)
    select @item

     --do your stuff here with @item 
     exec p_MyInnerProcedure @item 

    set @i = CHARINDEX(',',@list,@i)+1
    if(@i = 0) set @i = LEN(@list) 
end