Speed issues with While loops in SQL stored procedures - sql

Question

I'm taking over some code that is trying to store a list of IDs at one time and I find this code to be running quite slow for the actions we are trying to complete. Plus, in certain occasions resulting in deadlocks due to high amounts ids.
USE [store]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[UpdateImagePriority]
#separator CHAR(1),
#filename varchar(50),
#parentId int,
#slaveIds varchar(8000)
AS
BEGIN
SET NOCOUNT ON
DECLARE #SLAPriorityint
DECLARE #separator_position INT
DECLARE #array_value VARCHAR(50)
SET #slaveIds = #slaveIds + #separator
SET #SLAPriority= 0
WHILE PATINDEX('%' + #separator + '%', #slaveIds ) <> 0
BEGIN
SET #SLAPriority= #SLAPriority+ 1
SELECT #separator_position = PATINDEX('%' + #separator + '%',#slaveIds )
SELECT #array_value = LEFT(#slaveIds , #separator_position - 1)
SELECT Array_Value = #array_value
SELECT #slaveIds = STUFF(#slaveIds , 1, #separator_position, '')
UPDATE image_info
SET SLA_PRIORITY = #SLAPriority
WHERE FILE=#filename and EXT_PAR_ID=#parentId and SLA_ID=#array_value
END
SET NOCOUNT OFF
END
This is a sample of what we would pass in:
e.g.
separator = ','
filename = 'burgerking'
parentId = '1859'
slaveIds = '15,16,19,20,21,25,28,29,30,38,99'
Any suggestions on how to improve the speed of this code.
Thanks in advance!

Answer 1

What you are looking for is a table-valued function to split your values into a table. Then all you need is a single UPDATE .. FROM .. JOIN statement.
CREATE PROCEDURE [dbo].[UpdateImagePriority]
#separator CHAR(1),
#filename varchar(50),
#parentId int,
#slaveIds varchar(8000)
AS
set #slaveIds = #slaveIds + #separator
;WITH SplitString AS
(
SELECT
1 ID,LEFT(#slaveIds,CHARINDEX(',',#slaveIds)-1) AS Part,RIGHT(#slaveIds,LEN(#slaveIds)-CHARINDEX(',',#slaveIds)) AS Remainder
UNION ALL
SELECT
ID+1,LEFT(Remainder,CHARINDEX(',',Remainder)-1),RIGHT(Remainder,LEN(Remainder)-CHARINDEX(',',Remainder))
FROM SplitString
WHERE Remainder IS NOT NULL AND CHARINDEX(',',Remainder)>0
)
update i
SET SLA_PRIORITY = s.ID
from splitstring s
join image_info i on i.[FILE]=#filename and i.EXT_PAR_ID=#parentId and i.SLA_ID= s.Part
where s.Part > ''
For SQL Server 2000, or just to make the string splitting re-usable, I lifted this function from another question.
create function dbo.SplitString
(
#str varchar(8000),
#separator char(1)
)
returns table
AS
return (
with tokens(p, a, b) AS (
select
1,
1,
charindex(#separator, #str)
union all
select
p + 1,
b + 1,
charindex(#separator, #str, b + 1)
from tokens
where b > 0
)
select
p Id,
substring(
#str,
a,
case when b > 0 then b-a ELSE 8000 end)
AS Part
from tokens
)
GO
Then your SP becomes
CREATE PROCEDURE [dbo].[UpdateImagePriority]
#separator CHAR(1),
#filename varchar(50),
#parentId int,
#slaveIds varchar(8000)
AS
update i
SET SLA_PRIORITY = s.ID
from dbo.splitstring(#slaveIds,#separator) s
join image_info i on i.[FILE]=#filename and i.EXT_PAR_ID=#parentId and i.SLA_ID= s.Part
where s.Part > ''
GO

Answer 2

Use a function to convert the array into an XML document, which is then easy to return as a single column table of integers:
use tempdb
go
create function dbo.ParseIDs(#ids varchar(max), #separator char(1)) returns #rtn table (
id int
)
as
begin
declare #xml xml
set #xml = '<root><n>' + replace(#ids, #separator, '</n><n>') + '</n></root>'
insert into #rtn
select id.value('.', 'int')as id
from #xml.nodes('/root/n') as records(id)
return
end
go
declare #buf varchar(max) = '15,16,19,20,21,25,28,29,30,38,99'
select * from dbo.ParseIDs(#buf, ',')
go
drop function dbo.ParseIDs
go
This returns the following:
id
----
15
16
19
20
21
25
28
29
30
38
99
It would be easy to then to do something like this:
UPDATE image_info
SET SLA_PRIORITY = #SLAPriority
WHERE FILE=#filename and EXT_PAR_ID=#parentId and SLA_ID in (
select id from dbo.ParseIDs(#array_value, ',')
)
This might even be better:
UPDATE tbl
SET tbl.SLA_PRIORITY = #SLAPriority
FROM dbo.ParseIDs(#array_value, ',') as x
inner join image_info tbl on x.id = tbl.SLA_ID
WHERE tbl.FILE=#filename and tbl.EXT_PAR_ID=#parentId

Answer 3

Do a set based update:
USE [store]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[UpdateImagePriority]
#separator CHAR(1),
#filename varchar(50),
#parentId int,
#slaveIds varchar(8000)
AS
BEGIN
SET NOCOUNT ON
DECLARE #SLAPriorityint
DECLARE #separator_position INT
DECLARE #array_value VARCHAR(50)
SET #slaveIds = #slaveIds + #separator
SET #SLAPriority= 0
DECLARE #slaveIdTable Table
(
ids INT,
SlaPriority INT
)
WHILE PATINDEX('%' + #separator + '%', #slaveIds ) <> 0
BEGIN
SET #SLAPriority= #SLAPriority+ 1
SELECT #separator_position = PATINDEX('%' + #separator + '%',#slaveIds )
SELECT #array_value = LEFT(#slaveIds , #separator_position - 1)
-- get table of ids
INSERT INTO #slaveIdTable (ids,SlaPriority) VALUES(#array_value,#SLAPriority);
SELECT #slaveIds = STUFF(#slaveIds , 1, #separator_position, '')
END
UPDATE ii
SLA_PRIORITY = #SLAPriority
FROM image_info ii
JOIN #slaveIdTable st ON st.ids = st.SLA_ID
WHERE
st.[FILE] = #filename AND
st.EXT_PAR_ID = #parentId
SET NOCOUNT OFF
END
Richard's answer is a bit more elegant. Didn't see it while I was working on mine.