That's probably because you need to handle the character as part of a unicode string. It's not the same to have '_--' than to have N'_--'. You should also use...

Unless anyone has a better idea.

DECLARE @data TABLE(
  id int,
  grp int
);
INSERT INTO @data
VALUES ( 100,1), ( 101,1), ( 102,1), (...

If you're looking for valid dates and you're using SQL Server 2014, you could simply try to convert them.

SELECT TRY_CONVERT( date, CONVERT( char(8), SomeDateInteger), 112)

What about removing the temp table from the code?

LOAD *;
SQL
SELECT de.pate_tempor,
   de.prod_codigo,
   concepto = Convert(char(50),'FOB Fruta Exportacion'),...

Drop the "var", just use char(8).

Why do you have IDs that are that long? If an ID is 1509 characters long, it might have lost its purpose.
Instead of going for Full Text Search, which...

Here's a different way. It might be better or worse, so you should test.

WITH CTE AS(
  SELECT class, COUNT(item_id) Item_count
  FROM jc_item_class
 ...