[英]Loop Through a Table to concatenate Rows
我有一个类似结构的表:
Name Movies_Watched
A Terminator
B Alien
A Batman
B Rambo
B Die Hard
....
我试图得到这个:
Name Movies_Watched
A Terminator;Batman
B Alien, Die Hard, Rambo
我最初的猜测是:
SELECT Name, Movies_Watched || Movies_Watched from TABLE
但这显然是错误的。 有人可以告诉我如何遍历第二列并将它们连接起来吗? 逻辑如何?
知道group_concat是正确的方法。 但是还没有弄清楚。 当我尝试过:
select name, group_concat(movies_watched) from table group by 1
但它引发错误,表明用户定义的转换函数group_concat必须具有over子句
您正在寻找string_agg()
:
select name, string_agg(movie_watched, ';') as movies_watched
from t
group by name;
就是说,您正在使用Postgres,因此您应该学习如何使用数组而不是字符串来处理此类事情。 例如,当电影名称使用分号时,就不会与数组混淆。 那将是:
select name, array_agg(movie_watched) as movies_watched
from t
group by name;
使用array_agg
SELECT Name, array_agg(Movies_Watched)
FROM data_table
GROUP BY Name
我认为您在使用vertica upper时需要listagg或group_concat是postgrey解决方案
SELECT Name, listagg(Movies_Watched)
FROM data_table
GROUP BY Name
要么
select Name,
group_concat(Movies_Watched) over (partition by Name order by name) ag
from mytable
如前所述,在Vertica中,它是LISTAGG():
WITH
input(nm,movies_watched) AS (
SELECT 'A','Terminator'
UNION ALL SELECT 'B','Alien'
UNION ALL SELECT 'A','Batman'
UNION ALL SELECT 'B','Rambo'
UNION ALL SELECT 'B','Die Hard'
)
SELECT
nm AS "Name"
, LISTAGG(movies_watched) AS movies_watched
FROM input
GROUP BY nm;
-- out Name | movies_watched
-- out ------+----------------------
-- out A | Terminator,Batman
-- out B | Alien,Rambo,Die Hard
-- out (2 rows)
-- out
-- out Time: First fetch (2 rows): 12.735 ms. All rows formatted: 12.776 ms
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