union和Union All的區(qū)別?http://blog.csdn.net/wanghai__/article/details/4712555/

case when 語句 select case when NR='增城' Then '增城市' when NR='從化' Then NR='從化' Then '從化市' Else NR END detail from xxxxx where bm='2'

查詢符合條件的或者沒有條件的：Select ?count(*) ?From XXXX t where (To_Char(Create_Time, 'yyyy-MM-dd') >= '2014-01-01' Or ?'2014-01-01'Is Null) And (To_Char(Create_Time, 'yyyy-MM-dd') <='2014-04-30' Or '2014-04-30' Is Null)