postgresql数据合并,多条数据合并成1条的操作

sql:select max(de.bid_num) report_num,concat(to_char(to_timestamp(concat(ru.trade_date,' ',de.start_time), 'YYYY-MM-DD HH24:mi') :: TIMESTAMP WITHOUT TIME ZONE, 'HH24 '),':00') dd from quote_trade_rule ru LEFT JOIN quote_trade_rule_detail de on ru.trade_rule_id = de.trade_rule_id
WHERE
  1 = 1
AND ru.market_id ='a29c81ed-2baf-4c42-881a-f1e64a41e1b0'
AND to_char(ru.trade_date, 'YYYY-MM-DD') ='2018-10-17'
AND ru.rule_type ='2' GROUP BY dd ,trade_date ORDER BY dd,trade_date

highgo=# explain select people.id from people,dept01 where people.id=dept01.deptno;
                      QUERY PLAN
-------------------------------------------------------------------------------------------------
 Merge Join (cost=0.86..64873.59 rows=1048576 width=4)
  Merge Cond: (people.id = dept01.deptno)
  -> Index Only Scan using people_pkey on people (cost=0.44..303935.44 rows=10000000 width=4)
  -> Index Only Scan using idx_deptno on dept01 (cost=0.42..51764.54 rows=1048576 width=2)
(4 行记录)

highgo=# explain select people.id from people,dept01 where people.id=dept01.deptno;
                      QUERY PLAN
-------------------------------------------------------------------------------------------------
 Merge Join (cost=136112.80..154464.29 rows=1048576 width=4)
  Merge Cond: (people.id = dept01.deptno)
  -> Index Only Scan using people_pkey on people (cost=0.44..303935.44 rows=10000000 width=4)
  -> Materialize (cost=136112.36..141355.24 rows=1048576 width=2)
     -> Sort (cost=136112.36..138733.80 rows=1048576 width=2)
        Sort Key: dept01.deptno
        -> Seq Scan on dept01 (cost=0.00..16918.76 rows=1048576 width=2)
(7 行记录)