在T-SQL中创建循环函数

Question

i have a table include three fields tblUser(ID, parentID,count). parentID references tblUser(ID)

I want create function with parameter is ID in table. The function will select parentID and set count = count + 1 where ID = parentID .

I want to use while loop or for() to repeat the action until ID == parentID

Answer 1

Generally you want to avoid using loops in SQL. It's better to deal with data as a set rather than a row at a time, as loops are far more resource intensive.

Also, in the example you have given you haven't stated why you need to use a loop. It seems in this case it would be easier to simply say

set Count = ParentID

Now that I have warned you off using a loop, here's a simple example of a while loop:

Declare @Count integer = 0
  ,@ParentID integer

Select @ParentID = ParentID From Table 
(your where clause goes here)

While @Count <= @ParentID
BEGIN

  (whatever you want to do in your loop)
  Set @Count = @Count + 1

END

Answer 2

As far as I understand your problem, couldn't you just do it in a single statement?

update theTable
set count = count + 1
where ID = parentID

As Aidan said, generally you do NOT want to loop in SQL, nor do you generally need to.

Answer 3

SQL is a declarative language, you tell it what you want and let the query engine decide how best to do it

CREATE PROCEDURE IncrementCount @parentID int
AS
UPDATE theTable
SET count = count + 1
WHERE ID = parentID