在oracle查詢中重複使用子查詢

Question

我在更大的Oracle SQL查詢中多次列出與子查詢相同的查詢。有沒有一種方法來定義它，並使用更短的形式重用它？

Answer 1

您可以使用公用表表達式。從這裏

複製的查詢：Creating a CTE in Oracle

with RTG_YEARS (YR) as (
    select to_date('2013-01-01', 'yyyy-mm-dd') from dual 
    union all select to_date('2013-12-31', 'yyyy-mm-dd') from dual 
    union all select to_date('2014-01-01', 'yyyy-mm-dd') from dual 
    union all select to_date('2014-12-31', 'yyyy-mm-dd') from dual 
    union all select to_date('2015-01-01', 'yyyy-mm-dd') from dual 
    union all select to_date('2015-12-31', 'yyyy-mm-dd') from dual 
) 
select * 
from RTG_YEARS 
cross join RTG_YEARS;