Getting error when varchar value used in select query - sql

Question

I have a table named 'TABLE_RELATION'. I want to use some of relation codes to filter values from a select query. But when I am trying using IN operator getting an error Conversion failed when converting the varchar value ''301','302','303','304','305','306','312'' to data type smallint.
RELATION_CODE column is type smallint.
declare #guar_tab varchar(max)
declare #guar_tab_VALUES varchar(max)
select #guar_tab=COALESCE(''+#guar_tab+''',''','''')+convert(varchar(100), RELATION_CODE) from TABLE_RELATION where RELATION_CODE>300 and RELATION_CODE<400
SET #guar_tab_VALUES=(select #guar_tab)+''''+''
SELECT #guar_tab_VALUES
select * from TABLE_RELATION where RELATION_CODE in ( #guar_tab_VALUES)
When I tried '301','302','303','304','305','306','312' instead of #guar_tab_VALUES, it is working fine.
How can I solve this issue?
Any help will be appreciated.

Answer 1

You cannot pass a list of values like this. You are passing in a string with a single value that happens to have a bunch of commas.
One simplish method for your code is to use dynamic SQL:
declare #sql nvarchar(max);
set #sql = '
select *
from TABLE_RELATION
where RELATION_CODE in (#guar_tab_VALUES);
';
set #sql = replace(#sql, '#guar_tab_VALUEs', #guar_tab_VALUEs);
exec sp_executesql #sql;

Answer 2

Looking at your query, but I feel I'm missing something. What's wrong with just:
SELECT *
FROM TABLE_RELATION
WHERE RELATION_CODE > 300 AND RELATION_CODE < 400;
You're creating a delimited list of values from the table TABLE_RELATION, and then returning all those rows. There's literally no point. Based on what we have there's no need for dynamic SQL, or an IN.
We could express what you've written as:
SELECT *
FROM TABLE_RELATION TR
WHERE TR.RELATION_CODE IN (SELECT sq.RELATION_CODE
FROM TABLE_RELATION sq
WHERE sq.RELATION_CODE > 300
AND sq.RELATION_CODE < 400);
--or
SELECT *
FROM TABLE_RELATION TR
WHERE EXISTS (SELECT 1
FROM TABLE_RELATION sq
WHERE sq.RELATION_CODE > 300
AND sq.RELATION_CODE < 400
AND TR.RELATION_CODE = sq.RELATION_CODE);
As you can see, there's no need for the subquery,just put it in the main WHERE.

Answer 3

First of all, it's list of numbers.
So something like this
select * from table1
where col1 in ('1', '2', '3')
can be written as
select * from table1
where col1 IN (1, 2, 3)
But IN accepts a list of values, or a query that returns a list of values.
So just adding 1 string with values just won't do.
F.e. this won't work if col1 is a number.
select * from table1 where col1 IN ('1,2,3')
Because the string '1,2,3' can't be implicitly converted to a number.
Using a query could work
select * from table1
where col1 IN (select n from nums where n between 1 and 9)
If you do want use a variable that contains a list of numbers?
Then using a table variable might be for you.
DECLARE #NumTbl TABLE (n smallint primary key);
INSERT INTO #NumTbl (n)
SELECT DISTINCT RELATION_CODE
FROM TABLE_RELATION
WHERE RELATION_CODE > 300
AND RELATION_CODE < 400;
declare #guar_tab_values varchar(max);
select #guar_tab_values = concat(#guar_tab_values+', ', n) from #NumTbl order by n;
select #guar_tab_values as guar_tab_values;
SELECT *
FROM TABLE_RELATION
WHERE RELATION_CODE IN (select n from #NumTbl);
In your case I would just use those criteria in the WHERE clause.
SELECT *
FROM TABLE_RELATION
WHERE RELATION_CODE > 300
AND RELATION_CODE < 400

Answer 4

Such requirement comes many times in many different scenarios. so why not create generic solution.
We can a create user define function to slit comma separated string and return data in form of table.
Generic User Define Function :
-- FUNCTION TO SPLIT STRINGS.
ALTER FUNCTION [dbo].[SplitString]
( #stringToSplit VARCHAR(MAX) )
RETURNS
#returnList TABLE ([Name] [nvarchar] (500))
AS
BEGIN
DECLARE #name NVARCHAR(255)
DECLARE #pos INT
WHILE CHARINDEX(',', #stringToSplit) > 0
BEGIN
SELECT #pos = CHARINDEX(',', #stringToSplit)
SELECT #name = SUBSTRING(#stringToSplit, 1, #pos-1)
INSERT INTO #returnList
SELECT #name
SELECT #stringToSplit = SUBSTRING(#stringToSplit, #pos+1, LEN(#stringToSplit)-#pos)
END
INSERT INTO #returnList
SELECT #stringToSplit
RETURN
END
Call use define function:
declare #guar_tab varchar(max)
declare #guar_tab_VALUES varchar(max)
select #guar_tab=COALESCE(''+#guar_tab+',','')+convert(varchar(100), RELATION_CODE) from TABLE_RELATION where RELATION_CODE>300 and RELATION_CODE<400
select * from TABLE_RELATION where RELATION_CODE in (SELECT[Name] FROM dbo.SplitString( #guar_tab))
I hope this will help you :)