oracle timestamp轉換date及date型別相減

--timestamp轉換為date(ts欄位為timestamp型別)
SELECT cast(ts AS DATE) from tab1 WHERE tid=1;
--timestamp轉換為date(ts欄位為timestamp型別)
SELECT cast(ts AS DATE) from tab1 WHERE tid=3;
--date相減
SELECT (SELECT cast(ts AS DATE) from tab1 WHERE tid=3)-(SELECT cast(ts AS DATE) from tab1 WHERE tid=1) FROM dual;
--把date轉換為妙
SELECT ((SELECT cast(ts AS DATE) from tab1 WHERE tid=3)-(SELECT cast(ts AS DATE) from tab1 WHERE tid=1))*24*60*60 FROM dual;