我有一个简单的Postgres数据集,如下所示:
INSERT INTO mytable (day, person)
values
('Monday', 'A'),
('Monday', 'B'),
('Tuesday', 'A'),
('Thursday', 'B');
然后我运行一个产生两个array_aggs的查询,如下所示:
SELECT *
FROM (select day as d1,
array_agg(distinct person) as agg1
from mytable
group by day) AS AA
cross join
(select day as d2,
array_agg(distinct person) as agg2
from mytable
group by day) AS BB
产生这个数据集:
Monday, {A,B}, Monday, {A,B}
Monday, {A,B}, Thursday, {B}
Monday, {A,B}, Tuesday, {A}
Thursday, {B}, Monday, {A,B}
Thursday, {B}, Thursday, {B}
Thursday, {B}, Tuesday, {A}
Tuesday, {A}, Monday, {A,B}
Tuesday, {A}, Thursday, {B}
Tuesday, {A}, Tuesday, {A}
我想在此查询中添加第五列,用于标识每行中agg1和agg2中的重复条目数。
因此,例如,第一行将是2,第二行将是1.我希望如下所示,但这给了我一个模糊的语法错误:
SELECT *, count(select unnest(agg1) intersect select unnest(agg2))
FROM (select day as d1,
array_agg(distinct person) as agg1
from mytable
group by day) AS AA
cross join
(select day as d2,
array_agg(distinct person) as agg2
from mytable
group by day) AS BB
Postgresql有LATERAL。
可用于对记录级别的字段内容执行某些操作。
create table mytable (day varchar(30), person varchar(1));
INSERT INTO mytable (day, person) values ('Monday', 'A'), ('Monday', 'B'), ('Tuesday', 'A'), ('Thursday', 'B');
SELECT * FROM ( select day as d1, array_agg(distinct person) as agg1 from mytable group by day) AS AA cross join (select day as d2, array_agg(distinct person) as agg2 from mytable group by day ) AS BB CROSS JOIN LATERAL ( SELECT COUNT(*) AS MatchingPersons FROM ( SELECT unnest(agg1) person INTERSECT SELECT unnest(agg2) ) q ) lat
d1 | agg1 | d2 | agg2 | matchingpersons :------- | :---- | :------- | :---- | --------------: Monday | {A,B} | Monday | {A,B} | 2 Thursday | {B} | Monday | {A,B} | 1 Tuesday | {A} | Monday | {A,B} | 1 Monday | {A,B} | Thursday | {B} | 1 Thursday | {B} | Thursday | {B} | 1 Tuesday | {A} | Thursday | {B} | 0 Monday | {A,B} | Tuesday | {A} | 1 Thursday | {B} | Tuesday | {A} | 0 Tuesday | {A} | Tuesday | {A} | 1
db <>小提琴here
使用this answer中的函数,您可以编写:
SELECT *, array_length(array_intersect(arr1, arr2), 1) AS repeat_count
FROM /* your query */