T-SQL: Looping through an array of known values - sql

Question

Here's my scenario:
Let's say I have a stored procedure in which I need to call another stored procedure on a set of specific ids; is there a way to do this?
i.e. instead of needing to do this:
exec p_MyInnerProcedure 4
exec p_MyInnerProcedure 7
exec p_MyInnerProcedure 12
exec p_MyInnerProcedure 22
exec p_MyInnerProcedure 19
Doing something like this:
*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
My Main goal here is simply maintainability (easy to remove/add id's as the business changes), being able to list out all Id's on a single line... Performance shouldn't be as big of an issue

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

What I do in this scenario is create a table variable to hold the Ids.
Declare #Ids Table (id integer primary Key not null)
Insert #Ids(id) values (4),(7),(12),(22),(19)
-- (or call another table valued function to generate this table)
Then loop based on the rows in this table
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
or...
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
Either of above approaches is much faster than a cursor (declared against regular User Table(s)). Table-valued variables have a bad rep because when used improperly, (for very wide tables with large number of rows) they are not performant. But if you are using them only to hold a key value or a 4 byte integer, with a index (as in this case) they are extremely fast.

Answer 3

use a static cursor variable and a split function:
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
Cursors have a bad rep since the default options when declared against user tables can generate a lot of overhead.
But in this case the overhead is quite minimal, less than any other methods here. STATIC tells SQL Server to materialize the results in tempdb and then iterate over that. For small lists like this, it's the optimal solution.

Answer 4

You can try as below :
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

Answer 5

I usually use the following approach
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 6

CREATE TABLE #ListOfIDs (IDValue INT)
DECLARE #IDs VARCHAR(50), #ID VARCHAR(5)
SET #IDs = #OriginalListOfIDs + ','
WHILE LEN(#IDs) > 1
BEGIN
SET #ID = SUBSTRING(#IDs, 0, CHARINDEX(',', #IDs));
INSERT INTO #ListOfIDs (IDValue) VALUES(#ID);
SET #IDs = REPLACE(',' + #IDs, ',' + #ID + ',', '')
END
SELECT *
FROM #ListOfIDs

Answer 7

Make a connection to your DB using a procedural programming language (here Python), and do the loop there. This way you can do complicated loops as well.
# make a connection to your db
import pyodbc
conn = pyodbc.connect('''
Driver={ODBC Driver 13 for SQL Server};
Server=serverName;
Database=DBname;
UID=userName;
PWD=password;
''')
cursor = conn.cursor()
# run sql code
for id in [4, 7, 12, 22, 19]:
cursor.execute('''
exec p_MyInnerProcedure {}
'''.format(id))