SQL wildcard search

Hi.  I have an SQL question that I'm hoping I can get help on.

I am trying to find all records in a file where FLDA contains an
underscore ('_').  Here is my select statement:

SELECT * FROM FILEA WHERE FLDA LIKE '%_%'

Unfortunately, it returns every record in the file - and none of them
have an underscore in the field.

I eventually had to go character by character, like this:

SELECT * FROM FILEA WHERE SUBSTR(FLDA, 1, 1) = '_'

...and so on through the entire field.

But why didn't the LIKE search work?  If I change the underscore to a
'#' and run the same statement, it works just fine:

SELECT * FROM FILEA WHERE FLDA LIKE '%#%'

Is there something special about an underscore in a LIKE statement that
I didn't know about?

Thanks.

David Bocian