Convert int in string to integers in T-SQL

Question

I need to convert string to integers, but I'm getting a type error.

declare @stringinteger nvarchar(255) null;
set @stringinteger='1,2,3,4'

select *
from user
where id in (@stringinteger) 

The error I get:

Conversion failed when converting the nvarchar value '1,2,3,4' to data type int

Answer 1

You have two methods to handle this, dynamic SQL and splitting the string.

For the latter, you can use string_split() (introduced in SQL Server 2016) or a similar function (they are all over the web, google "string split sql server"):

select *
from user
where id in (select cast(value as int) from string_split(@stringinteger, ',')) ;

The dynamic SQL looks like:

declare @stringinteger nvarchar(255) null;
set @stringinteger = '1,2,3,4';

declare @sql nvarchar(max);
set 'select *
from user
where id in (@stringinteger)';

set @sql = replace(@sql, '@stringinteger', @stringinteger);

exec sp_executesql @sql;

Note that in SQL Server, you should always provide a length for character types. If you leave it out, then the default varies by context -- and your code may not do what you expect.