LIKE operator

Hi,

With mSQL I used to perform queries like below from within PHP:

select field1, field2 from table1 where field1 like '%$some_variable%'

where the '%' in the LIKE clause matches 0 or more characters of any value.
That is, the query above would match the strings that contain
'$some_variable' OR any string if $some_variable is empty.

For example: my table has two rows with the first record containing
field1='abc' and the second record containing field1='cde'.

If '$some_variable' is empty, then my query would return both rows.
If $some_variable='bc', then the query would return only the row where
field1='abc'.

With PostgreSQL I experience the following:

If '$some_variable' is empty, then my query returns *nothing*.
If $some_variable='bc', then the query would return only the row where
field1='abc'.

As the value of '$some_variable' is to be filled by some user while posting
a form, I don't know in advance if it is going to be empty or not.

How can I make the query results to be exactly as with mSQL without having
to alter my query 'throwing out' every part of the 'where' clause where
'$some_variable' is empty?

TIA,

Paulo
pparola(at)brazilinfo(dot)com