Oracle 查询出来的数据取第一条
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转载自：http://www.itpub.net/thread-246442-1-1.html
select * from (select * from <table> order by <key>) where rownum=1;
select * from (select * from <table> order by <key> desc) where rownum=1;
delete from tbl where a='a' and b='b' and c='c';