Group

名称

分组算子

介绍

对已经排好序的数据进行分组操作

说明

                        --清理环境
                        DROP TABLE t1 CASCADE;

--创建环境
CREATE TABLE t1(a int);
INSERT INTO t1 SELECT generate_series(1,10);
ANALYZE t1;

EXPLAIN ANALYZE SELECT a FROM t1 GROUP BY a ORDER BY a;
                                                       QUERY PLAN
--------------------------------------------------------------------------------------------------------
 Group  (cost=7.27..7.32 rows=10 width=4) (actual time=0.05..0.06 rows=10 loops=1)
   Group Key: A
   ->  Sort  (cost=7.27..7.29 rows=10 width=4) (actual time=0.05..0.05 rows=10 loops=1)
         Sort Key: A
         Sort Method: quicksort  Memory: 2kB
         ->  Seq Scan on T1  (cost=0.00..7.10 rows=10 width=4) (actual time=0.02..0.03 rows=10 loops=1)
 Planning Time: 0.12 msec
 Execution Time: 0.46 msec
(8 rows)