I run postgres 9.4, and want to migrate column in my database table to hstore just to be able to make performance comparison.
My current column is key-value pair in jsonb, w/o nested structure.
Any tips how to approach this problem?
Example data:
create table jsons (id int, val jsonb);
insert into jsons values
(1, '{"age":22}'),
(2, '{"height":182}'),
(3, '{"age":30, "height":177}');
Split json objects to key, value pairs:
select id, (jsonb_each_text(val)).key, (jsonb_each_text(val)).value
from jsons
id | key | value
----+--------+-------
1 | age | 22
2 | height | 182
3 | age | 30
3 | height | 177
(4 rows)
Aggregate the pairs and convert them to hstore:
select id, hstore(array_agg(key), array_agg(value))
from (
select id, (jsonb_each_text(val)).key, (jsonb_each_text(val)).value
from jsons
) sub
group by 1
order by 1
id | hstore
----+------------------------------
1 | "age"=>"22"
2 | "height"=>"182"
3 | "age"=>"30", "height"=>"177"
(3 rows)
The same can be accomplished in a more elegant way using lateral join:
select id, hstore(array_agg(key), array_agg(value))
from jsons
cross join jsonb_each_text(val)
group by 1
order by 1;
Related
i have a postgresql table t1 , id integer , data jsonb
id | data
--------------------
1 | {"1":{"11":11},"2":{"12":12}}
and i need a function to extract all key/value in separate rows
like this
key | values
----------------------
1 | {"11":11}
2 | {"12":12}
in "hstore" dataType , there was "hvals" function , do this
but in jsonb i dont find similar function
You are looking for jsonb_each
with t1 (id, data) as (
values (1, '{"1":{"11":11},"2":{"12":12}}'::jsonb)
)
select t.*
from t1, jsonb_each(data) as t(k,v)
returns:
k | v
--+-----------
1 | {"11": 11}
2 | {"12": 12}
In try to insert value from a hstore (postgreql) to a more generic table
In my car table, I have theses fields
id
fields (hstore)
My store table, I have theses fields
id
key
value
car_id
date
How to loop to my fields property in insert key, value to my store table.
Is there a way to do it with a select command?
Example data:
insert into car values
(1, 'brand=>ford, color=>yellow'),
(2, 'brand=>volvo, mileage=>50000, year=>2015');
Use the function each(hstore) to get pairs (key, value) of hstore column:
select id, key, value
from car, each(fields);
id | key | value
----+---------+--------
1 | brand | ford
1 | color | yellow
2 | year | 2015
2 | brand | volvo
2 | mileage | 50000
(5 rows)
The insert command may look like this:
insert into store (car_id, key, value)
select id, key, value
from car, each(fields);
I have a simple postgresql table that I'm tying to query. Imaging a table like this...
| ID | Account_ID | Iteration |
|----|------------|-----------|
| 1 | 100 | 1 |
| 2 | 101 | 1 |
| 3 | 100 | 2 |
I need to get the ID column for each Account_ID where Iteration is at its maximum value. So, you'd think something like this would work
SELECT "ID", "Account_ID", MAX("Iteration")
FROM "Table_Name"
GROUP BY "Account_ID"
And I expect to get:
| ID | Account_ID | MAX(Iteration) |
|----|------------|----------------|
| 2 | 101 | 1 |
| 3 | 100 | 2 |
But when I do this, Postgres complains:
ERROR: column "ID" must appear in the GROUP BY clause or be used in an aggregate function
Which, when I do that it just destroys the grouping altogether and gives me the whole table!
Is the best way to approach this using the following?
SELECT DISTINCT ON ("Account_ID") "ID", "Account_ID", "Iteration"
FROM "Marketing_Sparks"
ORDER BY "Account_ID" ASC, "Iteration" DESC;
The GROUP BY statement aggregates rows with the same values in the columns included in the group by into a single row. Because this row isn't the same as the original row, you can't have a column that is not in the group by or in an aggregate function. To get what you want, you will probably have to select without the ID column, then join the result to the original table. I don't know PostgreSQL syntax, but I assume it would be something like the following.
SELECT Table_Name.ID, aggregate.Account_ID, aggregate.MIteration
(SELECT Account_ID, MAX(Iteration) AS MIteration
FROM Table_Name
GROUP BY Account_ID) aggregate
LEFT JOIN Table_Name ON aggregate.Account_ID = Table_Name.Account_ID AND
aggregate.MIteration = Tabel_Name.Iteration
We have a PostgreSQL jsonb column containing hashes which in turn contain arrays of values:
id | hashes
---------------
1 | {"sources"=>["a","b","c"], "ids"=>[1,2,3]}
2 | {"sources"=>["b","c","d","e","e"], "ids"=>[1,2,3]}
What we'd like to do is create a jsonb query which would return
code | count
---------------
"a" | 1
"b" | 2
"c" | 2
"d" | 1
"e" | 2
we've been trying something along the lines of
SELECT jsonb_to_recordset(hashes->>'sources')
but that's not working - any help with this hugely appreciated...
The setup (should be a part of the question, note the proper json syntax):
create table a_table (id int, hashes jsonb);
insert into a_table values
(1, '{"sources":["a","b","c"], "ids":[1,2,3]}'),
(2, '{"sources":["b","c","d","e","e"], "ids":[1,2,3]}');
Use the function jsonb_array_elements():
select code, count(code)
from
a_table,
jsonb_array_elements(hashes->'sources') sources(code)
group by 1
order by 1;
code | count
------+-------
"a" | 1
"b" | 2
"c" | 2
"d" | 1
"e" | 2
(5 rows)
SELECT h, count(*)
FROM (
SELECT jsonb_array_elements_text(hashes->'sources') AS h FROM mytable
) sub
GROUP BY h
ORDER BY h;
We finally got this working this way:
SELECT jsonb_array_elements_text(hashes->'sources') as s1,
count(jsonb_array_elements_text(hashes->'sources'))
FROM a_table
GROUP BY s1;
but Klin's solution is more complete and both Klin and Patrick got there quicker than us (thank you both) - so points go to them.
So I have this table:
create table test (
id integer,
rank integer,
image varchar(30)
);
Then some values:
id | rank | image
---+------+-------
1 | 2 | bbb
1 | 3 | ccc
1 | 1 | aaa
2 | 3 | c
2 | 1 | a
2 | 2 | b
I want to group them by id and concatenate the image name in the order given by rank. In mySQL I can do this:
select id,
group_concat( image order by rank asc separator ',' )
from test
group by id;
And the output would be:
1 aaa,bbb,ccc
2 a,b,c
Is there a way I can have this in postgresql?
If I try to use array_agg() the names will not show in the correct order and apparently I was not able to find a way to sort them. (I was using postgres 8.4 )
In PostgreSQL 8.4 you cannot explicitly order array_agg but you can work around it by ordering the rows passed into to the group/aggregate with a subquery:
SELECT id, array_to_string(array_agg(image), ',')
FROM (SELECT * FROM test ORDER BY id, rank) x
GROUP BY id;
In PostgreSQL 9.0 aggregate expressions can have an ORDER BY clause:
SELECT id, array_to_string(array_agg(image ORDER BY rank), ',')
FROM test
GROUP BY id;