sql, using a subquery in the like operator - sql

Question

why does this work,
select*
from some_table
WHERE some_column_name like '%i%'
and not this?
select*
from some_table
WHERE
some_column_name like (select ''''+'%' +value +'%' + '''' as val
from [dbo].[fn_Split](' i this is a test testing Chinese undefined',' ')
where idx = 0)
I am trying to search for individual words instead of the whole phrase, the split function above will split the string on space characters and plug the results into a table with two columns, idx and value.

Answer 1

the LIKE operator takes a string for an argument. It cannot be used on a table, which I assume your function returns.
I think what you want to do is JOIN to the function, and then check where LIKE fn.Value:
select *
from some_table t
INNER JOIN (select value as val
from [dbo].[fn_Split](' i this is a test testing Chinese undefined',' ')
where idx = 0) f
ON t.some_column_name like '%'+f.val+'%'
If your subquery is guaranteed to only return one result, you could try putting the modulo symbols around it instead of inside it:
LIKE '%' + (YourSubQuery) + '%'

Answer 2

One possible reason is because you are appending single quotes onto the beginning and end of the string, and none of the values actually store single quotes in the string.
Another reason is might not work is because the subquery returns more than one row or zero rows. The function fn_split() is your own function, so I don't know what it returns. You have a subquery in a context where it can return at most one row and one column. That is called a scalar subquery. If the subquery returns more than one row, you will get an error. If the subquery returns no rows -- for instance, if idx starts counting at 1 rather than 0 -- then it will return NULL which fails the test.
If you want to find a match this way, I would recommend exists:
select t.*
from some_table t
where exists (select 1 as val
from [dbo].[fn_Split](' i this is a test testing Chinese undefined',' ') s
where s.idx = 0 and
t.some_column_name like '%' + value + '%'
);

Answer 3

The results of your sub-query is a literal string. The % symbol isn't seen as a wildcard. Also, does your functions return multiple rows? If so, LIKE operator can only evaluate a single value.
If your functions does return a single value, I would suggest looking into using Dynamic SQL. Something like the following:
DECLARE #SQL VARCHAR(MAX), #WildCard VARCHAR(MAX)
SELECT #WildCard = '%' + value + '%'
FROM [dbo].[fn_Split](' i this is a test testing Chinese undefined',' ')
WHERE idx = 0
SET #SQL = 'SELECT * FROM some_table WHERE some_column_name like ''' + #WildCardWildCard + ''''
EXEC(#SQL)