How to use IN clause in sql server so that it selects everything if nothing is provided for its list argument?

Question

Assume I have a sql query like this

SELECT * FROM TABLE where country in ('USA', 'UK')

This query works as expected that is it selects all rows where country column is either 'USA' or 'UK'. Now however, if I run this query

SELECT * FROM TABLE where country IN ()

its a syntax error. So I change it to run something like this

SELECT * FROM TABLE where country IN ('')

My goal here is to use jdbcTemplate of Spring framework to dynamically run this sql query. However I am not sure what my inputs are going to be. So I want to be able to pass the countries like 'USA' or 'UK' and get only rows related to those OR pass nothing and get ALL rows. So how do I get ALL rows if nothing is passed into IN clause?

Answer 1

So how do I get ALL rows if nothing is passed into IN clause?

You have to use dynamic sql.

e.g. Below is a simple example to get you started.

set nocount on
declare @sqltext nvarchar(max) = N''
declare @countryInput varchar(30)  

select @sqltext = N'
    select * -- good practice to use explicit column names 
        from dbo.Table
        where 1 =1 '
        + case when @countryInput is null or @countryInput ='' then ''
        else ' and country in (''USA'',''UK'')'
        end

        print @sqltext 

Answer 2

In SQL 2016 and later, you can use JSON for this without dynamic SQL.

You can have a static query like:

select *
from SomeTable
where @values is null or SomeCol in ( select value from openjson(@values) )

or

    if @values is null
    begin
      select *
      from SomeTable
    end
    else
    begin
      select *
      from SomeTable
      where SomeCol in ( select value from openjson(@values) )
    end

And bind @values to an nvarchar(max) parameter, formatted as a JSON array.

Answer 3

You should change your program to not send through the where clause rather than using dynamic SQL or JSON or some other technique. Add an if statement when building your code to control addding the WHERE country IN () statement.