我正在使用PostgreSQL 9.1并需要帮助将多行连接在一起。我需要在2个表中这样做。当我使用两次array_agg()
函数时,我在结果中得到重复的值。
表:
CREATE TABLE rnp (id int, grp_id int, cabinets varchar(15) );
INSERT INTO rnp VALUES
(1,'11','cabs1')
,(2,'11','cabs2')
,(3,'11','cabs3')
,(4,'11','cabs4')
,(5,'22','c1')
,(6,'22','c2');
CREATE TABLE ips (id int, grp_id int, address varchar(15));
INSERT INTO ips VALUES
(1,'11','NY')
,(2,'11','CA')
,(3,'22','DC')
,(4,'22','LA');
SQL:
SELECT DISTINCT
rnp.grp_id,
array_to_string(array_agg(rnp.cabinets)OVER (PARTITION BY rnp.grp_id), ',') AS cabinets,
array_to_string(array_agg(ips.address) OVER (PARTITION BY ips.grp_id), ',') AS addresses
FROM rnp JOIN ips ON rnp.grp_id=ips.grp_id
结果:
GRP_ID CABINETS ADDRESSES
11 cabs1,cabs1,cabs2,cabs2,cabs3,cabs3,cabs4,cabs4 NY,CA,NY,CA,NY,CA,NY,CA
22 c1,c1,c2,c2 DC,LA,DC,LA
我需要的是:
GRP_ID CABINETS ADDRESSES
11 cabs1,cabs2,cabs3,cabs4 NY,CA,
22 c1,c2 DC,LA
SQLFiddle中的这个例子:http://sqlfiddle.com/#!1/4815e/19
如果使用一个表 - SQLFiddle:http://sqlfiddle.com/#!1/4815e/20
,则没有问题我错过了什么?是否可以这样做,因为JOIN?
答案 0 :(得分:33)
使用查询级GROUP BY并与DISTINCT子句聚合,而不是使用窗口函数和修补:
SELECT
rnp.grp_id,
array_to_string(array_agg(distinct rnp.cabinets),',') AS cabinets,
array_to_string(array_agg(distinct ips.address),',') AS addresses
FROM rnp JOIN ips ON rnp.grp_id=ips.grp_id GROUP BY rnp.grp_id, ips.grp_id;
结果:
grp_id | cabinets | addresses
--------+-------------------------+-----------
11 | cabs1,cabs2,cabs3,cabs4 | CA,NY
22 | c1,c2 | DC,LA
(2 rows)
这里的关键是,不是使用窗口函数和修改,而是使用查询级GROUP BY
并使用DISTINCT
子句聚合。
这也适用于窗口函数方法,除了PostgreSQL(至少9.1)在窗口函数中不支持DISTINCT
:
regress=# SELECT DISTINCT
rnp.grp_id,
array_to_string(array_agg(distinct rnp.cabinets)OVER (PARTITION BY rnp.grp_id), ',') AS cabinets,
array_to_string(array_agg(distinct ips.address) OVER (PARTITION BY ips.grp_id), ',') AS addresses
FROM rnp JOIN ips ON rnp.grp_id=ips.grp_id;
ERROR: DISTINCT is not implemented for window functions
LINE 3: array_to_string(array_agg(distinct rnp.cabinets)OVER (PART...