问题
In pg, there is a tags field of type varchar
, containing tags separated by ]
, e.g 'a]b]c'
.
Need to count occurrences of these tags across multiple rows.
Currently, I know how to:
- Convert the raw string into pg array
['a', 'b', 'c']
- and if the column is given as jsonb object
{'a':1, 'b':1, 'c':1}
, could count frequency via jsonb functions.
But I don't know how to convert pg array ['a', 'b', 'c']
into jsonb object {'a':1, 'b':1, 'c':1}
, or just count frequency on array elements directly.
The questions are:
- A. How to convert text
'a]b]c'
into jsonb object{'a':1, 'b':1, 'c':1}
, with all values as1
. - B. How to count frequency of array elements
['a', 'b', 'c']
, across multiple rows.
If either of the 2 questions can be solved, the original problem could be solved.
Or, there are even a better solution?
@Update - To make the question more clear
If the input column is already json object, not raw string or array.
Following table show what I want to do:
-- create table,
create table json_aggr_learn (
id serial8 primary key,
uid int8,
freq jsonb,
created_at timestamptz default current_timestamp
);
-- init data
insert into json_aggr_learn(uid, freq) values
(1, '{"a":1, "b":2}'),
(1,'{"b":2, "c":4}'),
(2, '{"a":1, "b":2}'),
(2,'{"b":7, "c":4}'),
(2,'{"e":10, "c":4}'),
(3,'{"a":5, "c":4, "f":2}');
select * from json_aggr_learn limit 5;
-- aggr
select uid, jsonb_object_agg(key, value) as merged_freq
from
(select id, uid, key, value
from json_aggr_learn, jsonb_each_text(freq)
) as expended
group by uid
order by uid;
Here is the output of aggr sql:
回答1:
You can unnest() arrays, e.g.:
select id, jsonb_object_agg(tag, count) as tags
from (
select id, unnest(string_to_array(tags, ']')) as tag, count(*)
from my_table
group by 1, 2
) s
group by 1
order by 1
Db<>fiddle.
来源:https://stackoverflow.com/questions/65785117/postgresql-count-freuency-of-array-or-jsonb-object