Miscellany

SELECT *
FROM vkt_prog_erw
WHERE (
(
bis_datum >= CURRENT_DATE
OR datum >= CURRENT_DATE
)
AND (
( bis_datum <= DATE_ADD( CURRENT_DATE, INTERVAL 180 DAY ) AND bis_datum > '0000-00-00' )
OR ( datum <= DATE_ADD( CURRENT_DATE, INTERVAL 180 DAY ) AND datum > '0000-00-00' )
)
)