请高手帮我优化下下面这条语句
创意顽石 2007-05-28 06:17:13 SELECT a.PubBeginDate,a.PubEndDate,b.BookingDays
FROM SD_kind_main a,SD_Other_Parameters b
WHERE a.KindCode(+)=b.KindCode AND rownum<2 and b.KindCode='061703'
union
SELECT a.PubBeginDate,a.PubEndDate,b.BookingDays
FROM SD_kind_main a,SD_Other_Parameters b
WHERE a.KindCode(+)=b.KindCode AND rownum<2 and b.KindCode is null
a表是主表,b表是从表,b表的kindcode如果不为空的话,以kindcode为准,如果没有kindcode对应的值,则以空的值为准。