use_sortdistinct

确定查询使用sortagg算子实现distinct操作。

举例:

--  清理环境
DROP TABLE a CASCADE;

--  创建表
CREATE TABLE a(a1 INT, a2 INT);


explain select /*+ use_sortdistinct */ distinct a1 from a;
QUERY PLAN(text)      
----------------------
Unique  (cost=622.40..663.36 rows=200 width=4)
  ->  Sort  (cost=622.40..642.88 rows=8192 width=4)
        Sort Key: A1
        ->  Seq Scan on A  (cost=0.00..89.92 rows=8192 width=4)
总数目：4

--  删除表
DROP TABLE a CASCADE;