Building dynamic T-SQL query from a string argument in a sproc - sql

Question

Let's say I have a table which contains a varchar field:
CREATE TABLE [MyTable] (
[MyId] varchar(3) NOT NULL,
.....
)
The [MyId] column contains sequential alphanum values like A1, A2... A99, B1, B2..B99, C1 and so on (up to Z99).
What I'd like to do is to extract rows from the table whose MyId field matches some specific prefixes... e.g. I'd like to fetch rows from the series A, C, P and X.
And I'd like to this with a sproc which will dynamically construct the query based on the prefix alphabets supplied in the argument.
I'm thinking about something like this...
CREATE PROCEDURE [dbo].[uspFilterMyTable]
#prefixArray varchar(max)
AS
... -- split individual characters from #prefixArray into an array
SELECT * FROM [MyTable]
WHERE
[MyId] LIKE ....
OR
[MyId] LIKE .... -- iterate all characters from #prefixArray
I think the main bulk of the stored procedure will resemble the following pseudo-code:
DECLARE #sql nvarchar(max)
-- iterate through all the characters
SET #sql = 'SELECT * FROM [MyTable] WHERE [MyId] LIKE ' + #charInTheArray + '%'
SET #sql = #sql + ' OR [MyId] LIKE ' + #nextCharInArray + '%'
EXEC (#sql)
The above proecedure will be called like this:
EXEC uspFilterMyTable("A,C,P,X")
... or perhaps like this (if it makes splitting the alphabets easier):
EXEC uspFilterMyTable("ACPX")
Any ideas? Pointers?
Update: OK, this is what I've come up with ([Split] function borrowed from Chhatrapati Sharma):
-- [MyTable] contains these rows: 'A7', 'A87', 'B16', 'C51', 'H99', 'X12'
-- the "input" parameter
DECLARE #prefixArray NVARCHAR(100)= 'H,A,C'
-- split the string into SQL wild-card patterns
DECLARE charCursor CURSOR FOR
select items + N'%' from dbo.Split(#prefixArray, ',')
OPEN charCursor;
DECLARE #pattern CHAR(2)
-- create temp table if necessary
IF NOT EXISTS(SELECT * FROM TEMPDB.SYS.TABLES WHERE NAME LIKE '#tmpTable%')
CREATE TABLE #tmpTable ([Id] VARCHAR(3) NOT NULL)
-- purge old data
DELETE FROM #tmpTable
FETCH NEXT FROM charCursor into #pattern
WHILE ##FETCH_STATUS = 0
BEGIN
--SELECT * INTO #tmpTable FROM [MyTable] WHERE [MyId] LIKE #pattern
Insert Into #tmpTable Select * FROM [MyTable] WHERE [MyId] LIKE #pattern
FETCH NEXT FROM charCursor into #pattern
END
CLOSE charCursor;
DEALLOCATE charCursor;
-- return the values
SELECT * FROM #tmpTable
It's ugly I know, but it works... any tips to improvise the code?

Answer 1

first you should create below function and then use this in query like this
SELECT * FROM [MyTable] WHERE [MyId] in (select items from dbo.split(#prefixArray,','))
CREATE FUNCTION [dbo].[Split](#String varchar(8000), #Delimiter char(1))
returns #temptable TABLE (items varchar(8000))
as
begin
declare #idx int
declare #slice varchar(8000)
select #idx = 1
if len(#String)<1 or #String is null return
while #idx!= 0
begin
set #idx = charindex(#Delimiter,#String)
if #idx!=0
set #slice = left(#String,#idx - 1)
else
set #slice = #String
if(len(#slice)>0)
insert into #temptable(Items) values(#slice)
set #String = right(#String,len(#String) - #idx)
if len(#String) = 0 break
end
return
end

Answer 2

Here you have a nice and fast split method based on XML:
DECLARE #str NVARCHAR(100)= 'A1,B3,C4,B12,K19', #separator VARCHAR(1)= ','
DECLARE #SplitedList TABLE (code NVARCHAR(30))
DECLARE #XMLList XML
SET #XMLList=CAST('<i>'+REPLACE(#str, #separator,'</i><i>')+'</i>' AS XML)
INSERT INTO #SplitedList
SELECT x.i.value('(./text())[1]','varchar(100)')
FROM #XMLList.nodes('i') x(i)
SELECT * FROM #SplitedList
Result will be a table with the splitted values:
code
A1
B3
C4
B12
K19
From here you can continue and use this table on your procedure and join with you original table using LIKE as you propossed.

Answer 3

I would have suggested you to use table valued parameters to call your stored procedure. I guess you call it from .net. But EF I think will not be able to handle it, though you might check it. If not, I think the best way is to first parse the string into a temporary table, or a table value and after that join with it.
With TVP:
CREATE PROCEDURE [dbo].[uspFilterMyTable]
#prefixArray tvp_idlist readonly
as
select
t.*
from MyTable t
join #prefixArray pa on pa.id = t.myid
With a split function (of your choosing, you find many examples on the net)
CREATE PROCEDURE [dbo].[uspFilterMyTable]
#prefixArray varchar(max)
as
create #prefixArray tvp_idlist
insert into #prefixArray (id)
select id from dbo.myCustomSplit(#prefixArray,',')
select
t.*
from MyTable t
join #prefixArray pa on pa.id = t.myid
Where for both cases #prefixArray is a table variable is Id = varchar(3)
As an edit, after a little digging, it seems that with a little work EF works fine with TVPs. Check this : Entity Framework Stored Procedure Table Value Parameter. So The best thing is to send directly a table to your stored procedure, then to send a string to parse.