problem porting MySQL SQL to Postgres

I've stumbled across a query I don't quite understand the error message
for.

This query is pulled from a working MySQL setup:

SELECT
DEWEY_ID, DEWEY_HUNDREDS, DEWEY_TENS, DEWEY_ONES, DEWEY_POINT_ONES,
DEWEY_POINT_TENS,
DEWEY_POINT_HUNDREDS, DEWEY_POINT_THOUSANDS, DEWEY_TYPE, DEWEY_LANG,
DEWEY_SUBJECT FROM lu_dewey
WHERE
(DEWEY_HUNDREDS = 9) AND
(DEWEY_TENS >= 0) AND
(DEWEY_TENS <= 9) AND
(DEWEY_ONES = 0 || DEWEY_ONES = NULL) AND
(DEWEY_POINT_ONES = 0 || DEWEY_POINT_ONES = NULL) AND
(DEWEY_POINT_TENS = 0 || DEWEY_POINT_TENS = NULL) AND
(DEWEY_POINT_HUNDREDS = 0 || DEWEY_POINT_HUNDREDS = NULL) AND
(DEWEY_POINT_THOUSANDS = 0 || DEWEY_POINT_THOUSANDS = NULL) AND
(DEWEY_TYPE = 't') AND
(DEWEY_LANG = 'en')
ORDER BY DEWEY_TENS

However I'm getting the following error:

ERROR: Unable to identify an operator '=' for types 'character' and
'boolean' You will have to retype this query using an explicit cast.

Any help would be much appreciated

TIA
--
Dan Field