oracle常用函数及常用方法积累

1.oracle如何取前几条记录
select * from (select distinct emp_name from userTable) where rownum<10

2.oracle如何将日期转换成指定格式
select to_char(sysdate,'YYYY/mm/dd') mydate from tableName

3.oracle查找某条记录不为空或者为空
select * from tableName where col1 is not null and col2 is null

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