I'm trying to return a JSON object from postgres that looks something like this:
[
{id: 1, name: "some organisation name", alias: [{alias:"alt name"}, {alias:"another name"}]}
...]
My query below works fine, except that I want to add a where condition, referencing the org_aliases table
SELECT json_build_object('id', table1.id, 'name', table1.name, 'alias', a.alias) as json
FROM orgs table1
CROSS JOIN LATERAL (
SELECT json_agg(agg) AS alias
FROM (
SELECT table2.alias as name
FROM org_aliases table2
WHERE
table2.org_id = table1.id
) agg
) a
WHERE
table1.name ilike 'nspcc'
or table2.alias ilike 'nspcc';
It fails on the last line (missing from condition on table2). I can see why it doesn't allow me to do this, as I'm referencing something inside a sub query.
My question, is what's the best way to handle this?
My only idea is that I need to join the org_aliases again so I can add a where condition. But if anyone has a better idea for how I structure the query to avoid duplication, that would be amazing.
Not sure if it's exactly what you're looking for, but it does give you the required result for your example:
SELECT
json_build_object('id', orgs.id
, 'name', name
, 'alias', json_agg(
json_build_object('name', alias)
)
)
FROM orgs
LEFT JOIN org_aliases ON orgs.id = org_aliases.org_id
WHERE name ILIKE '%dave%'
OR alias ILIKE '%dave%'
GROUP BY
orgs.id, orgs.name;
Edit: I would use a CTE to first find my target id and then get alle the data that I need. This makes it easy to understand (and debug):
WITH target AS (
SELECT orgs.id
FROM orgs
LEFT JOIN org_aliases ON orgs.id = org_aliases.id
WHERE name ILIKE '%dave%'
OR alias ILIKE '%dave%'
)
SELECT
json_build_object('id', orgs.id
, 'name', name
, 'alias', json_agg(
json_build_object('name', alias)
)
)
FROM target
JOIN orgs ON target.id = orgs.id
LEFT JOIN org_aliases ON orgs.id = org_aliases.org_id
GROUP BY
orgs.id, orgs.name;
From here, and here I have figured out that if I want to aggregate a set of related rows into an array of objects I have to use this syntax:
(select to_json(C) from ( /* subquery */ ) C)
So, if I have three tables: user, creature and their junction table user_creature:
And I want to retrieve each user, and each creature that belongs to this user, I would have to do something like this:
select to_json(T)
from (
select "user".id as user_id,
(select to_json(C) -- !!! There it is
from (
select name, height
from creature
inner join "user_creature" uc on creature.id = "uc".creature_id
inner join "user" u on "uc".user_id = u.id
where u.id = user_id
) C) as "creatures" -- !!! There it is
from "user"
) T;
This query successfully retrieves a list of users and their related creatures:
Is there a way to drop select and from keywords from the query, so that I can write my query like this:
select to_json(T)
from (
select "user".id as user_id,
to_json( -- !!! Calling to_json directly on select statement
select name, height
from creature
inner join "user_creature" uc on creature.id = "uc".creature_id
inner join "user" u on "uc".user_id = u.id
where u.id = user_id
) as "creatures"
from "user"
) T;
It is possible to use a subquery as the argument to to_json, but not practical:
You need to wrap the subquery in a grouping parenthesis: to_json( (SELECT … FROM …) )
The subquery must return exactly one row (but that's normal)
The subquery must return exactly one column. This is a bit harder - you can return a record, but if you build it dynamically (e.g. from a selection of columns, you can hardly control the field names)
(See a demo here).
Instead, use json_build_object if you want to write a single SELECT query only:
SELECT json_build_object(
'user_id', u.id,
'creatures', (
SELECT json_build_object(
'name', c.name,
'height', c.height
)
FROM creature c
INNER JOIN "user_creature" uc ON c.id = uc.creature_id
WHERE uc.user_id = u.id
)
)
FROM "user" u;
And, if you want to be able to retrieve multiple rows use SELECT json_agg(json_build_object(…)) FROM … or ARRAY(SELECT json_build_object(…) FROM …):
SELECT json_build_object(
'user_id', u.id,
'creatures', (
SELECT json_agg(json_build_object(
'name', c.name,
'height', c.height
))
FROM creature c
INNER JOIN "user_creature" uc ON c.id = uc.creature_id
WHERE uc.user_id = u.id
)
)
FROM "user" u;
This is my query:
SELECT "vehicle"."id",
"vehicle"."description",
"tag"."id" AS "tag_id",
"tag"."name" AS "tag_name"
FROM "vehicle"
INNER JOIN "vehicle_tag_pivot" ON "vehicle"."id" = "vehicle_tag_pivot"."vehicle_id"
INNER JOIN "tag" ON "vehicle_tag_pivot"."tag_id" = "tag"."id"
WHERE "tag"."name" IN ('car', 'busses')
AND "vehicle"."category_id" = '1E4FD2C5-C32E-4E3F-91B3-45478BCF0185'
I only have one vehicle in my database. It has two tags -> car and busses (this is test data).
So when I run the query, it returns The exact same vehicle showing the 2 tags it has.
How do I get it to return the vehicle once? I do not really want to return the tag_name. I only want to filter and return all the vehicles that has the both tags car and busses. If one vehicle has both those tags, then it should return that vehicle only. But instead it is returning the same vehicle twice showing its tags.
This should work for you.
SELECT i.*
FROM "interest" as "i"
where i.id in (
select it.interest_id
from interest_tag_pivot it
join tag t on it.tag_id = t.id
where t.name in ('car', 'busses')
group by it.interest_id
having count (*) = 2
)
and i.category_id = '1E4FD2C5-C32E-4E3F-91B3-45478BCF0185'
Do not JOIN - joins leads to duplications. Put all tags logic to WHERE EXISTS(...) or similar.
Here two scalar subqueries comparison in WHERE, try this (important! - it is assumed that tags for each vehicle can't duplicate, so we can compare its counts):
WITH required_tags(val) AS (
VALUES ('car'),
('busses')
)
SELECT "vehicle"."id",
"vehicle"."description",
"tag"."id" AS "tag_id",
"tag"."name" AS "tag_name"
FROM "vehicle"
WHERE "vehicle"."category_id" = '1E4FD2C5-C32E-4E3F-91B3-45478BCF0185'
AND (
-- count matching tags...
SELECT count(1)
FROM "vehicle_tag_pivot"
INNER JOIN "tag" ON "vehicle_tag_pivot"."tag_id" = "tag"."id"
WHERE "vehicle"."id" = "vehicle_tag_pivot"."vehicle_id"
AND "tag"."name" IN (SELECT val FROM required_tags)
) = (
-- ...equals to count required tags
SELECT count(1)
FROM required_tags
)
I have a question regarding lateral joins in Postgres.
My use case is I want to return a dataset that combines multiple tables but limits the number of publications and reviews returned. The simplified table schema is below
Table Author
ID
NAME
Table Review
ID
AUTHOR_ID
PUBLICATION_ID
CONTENT
Table Publication
ID
NAME
Table AuthorPublication
AUTHOR_ID
PUBLICATION_ID
So for my initial query I have this:
SELECT
a.id,
a.name
json_agg (
json_build_object (
'id', r.id,
'content', r.content
)
) AS reviews,
json_agg (
json_build_object(
'id', p.id,
'name', p.name
)
) AS publications
FROM
public.author a
INNER JOIN
public.review r ON r.author_id = a.id
INNER JOIN
public.author_publication ap ON ap.author_id = a.id
INNER JOIN
public.publication p ON p.id = ap.publication_id
WHERE
a.id = '1'
GROUP BY
a.id
This returns the data I need, for example I get the author's name, id and a list of all of their reviews and publications they belong to. What I want to be able to do is limit the number of reviews and publications. For example return 5 reviews, and 3 publications.
I tried doing this with a lateral query but am running into an issue where if I do a single lateral query it works as intended.
so like:
INNER JOIN LATERAL
(SELECT r.* FROM public.review r WHERE r.author_id = a.id LIMIT 5) r ON TRUE
This returns the dataset with only 5 reviews - but if I add a second lateral query
INNER JOIN LATERAL
(SELECT ap.* FROM public.author_publication ap WHERE ap.author_id = a.id LIMIT 5) r ON TRUE
I now get 25 results for both reviews and publications with repeated/duplicated data.
So my question is are you allowed to have multiple lateral joins in a single PG query and if not what is a good way to go about limiting the number of results from a JOIN?
Thanks!
You must change your query to something like this:
SELECT
a.id,
a.name,
(
SELECT
json_agg ( r )
FROM (
SELECT
json_build_object (
'id', r.id,
'content', r.content
) AS r
FROM public.review r
WHERE r.author_id = a.id
ORDER BY r.id
LIMIT 5
) AS a
) AS reviews,
(
SELECT
json_agg (p)
FROM (
SELECT
json_build_object(
'id', p.id,
'name', p.name
) AS p
FROM public.author_publication ap
INNER JOIN public.publication p ON p.id = ap.publication_id
WHERE ap.author_id = a.id
ORDER BY p.id
LIMIT 3
) AS a
) AS publications
FROM
public.author a
WHERE
a.id = '1'
I'm trying to map the results of a query to JSON using the row_to_json() function that was added in PostgreSQL 9.2.
I'm having trouble figuring out the best way to represent joined rows as nested objects (1:1 relations)
Here's what I've tried (setup code: tables, sample data, followed by query):
-- some test tables to start out with:
create table role_duties (
id serial primary key,
name varchar
);
create table user_roles (
id serial primary key,
name varchar,
description varchar,
duty_id int, foreign key (duty_id) references role_duties(id)
);
create table users (
id serial primary key,
name varchar,
email varchar,
user_role_id int, foreign key (user_role_id) references user_roles(id)
);
DO $$
DECLARE duty_id int;
DECLARE role_id int;
begin
insert into role_duties (name) values ('Script Execution') returning id into duty_id;
insert into user_roles (name, description, duty_id) values ('admin', 'Administrative duties in the system', duty_id) returning id into role_id;
insert into users (name, email, user_role_id) values ('Dan', 'someemail#gmail.com', role_id);
END$$;
The query itself:
select row_to_json(row)
from (
select u.*, ROW(ur.*::user_roles, ROW(d.*::role_duties)) as user_role
from users u
inner join user_roles ur on ur.id = u.user_role_id
inner join role_duties d on d.id = ur.duty_id
) row;
I found if I used ROW(), I could separate the resulting fields out into a child object, but it seems limited to a single level. I can't insert more AS XXX statements, as I think I should need in this case.
I am afforded column names, because I cast to the appropriate record type, for example with ::user_roles, in the case of that table's results.
Here's what that query returns:
{
"id":1,
"name":"Dan",
"email":"someemail#gmail.com",
"user_role_id":1,
"user_role":{
"f1":{
"id":1,
"name":"admin",
"description":"Administrative duties in the system",
"duty_id":1
},
"f2":{
"f1":{
"id":1,
"name":"Script Execution"
}
}
}
}
What I want to do is generate JSON for joins (again 1:1 is fine) in a way where I can add joins, and have them represented as child objects of the parents they join to, i.e. like the following:
{
"id":1,
"name":"Dan",
"email":"someemail#gmail.com",
"user_role_id":1,
"user_role":{
"id":1,
"name":"admin",
"description":"Administrative duties in the system",
"duty_id":1
"duty":{
"id":1,
"name":"Script Execution"
}
}
}
}
Update: In PostgreSQL 9.4 this improves a lot with the introduction of to_json, json_build_object, json_object and json_build_array, though it's verbose due to the need to name all the fields explicitly:
select
json_build_object(
'id', u.id,
'name', u.name,
'email', u.email,
'user_role_id', u.user_role_id,
'user_role', json_build_object(
'id', ur.id,
'name', ur.name,
'description', ur.description,
'duty_id', ur.duty_id,
'duty', json_build_object(
'id', d.id,
'name', d.name
)
)
)
from users u
inner join user_roles ur on ur.id = u.user_role_id
inner join role_duties d on d.id = ur.duty_id;
For older versions, read on.
It isn't limited to a single row, it's just a bit painful. You can't alias composite rowtypes using AS, so you need to use an aliased subquery expression or CTE to achieve the effect:
select row_to_json(row)
from (
select u.*, urd AS user_role
from users u
inner join (
select ur.*, d
from user_roles ur
inner join role_duties d on d.id = ur.duty_id
) urd(id,name,description,duty_id,duty) on urd.id = u.user_role_id
) row;
produces, via http://jsonprettyprint.com/:
{
"id": 1,
"name": "Dan",
"email": "someemail#gmail.com",
"user_role_id": 1,
"user_role": {
"id": 1,
"name": "admin",
"description": "Administrative duties in the system",
"duty_id": 1,
"duty": {
"id": 1,
"name": "Script Execution"
}
}
}
You will want to use array_to_json(array_agg(...)) when you have a 1:many relationship, btw.
The above query should ideally be able to be written as:
select row_to_json(
ROW(u.*, ROW(ur.*, d AS duty) AS user_role)
)
from users u
inner join user_roles ur on ur.id = u.user_role_id
inner join role_duties d on d.id = ur.duty_id;
... but PostgreSQL's ROW constructor doesn't accept AS column aliases. Sadly.
Thankfully, they optimize out the same. Compare the plans:
The nested subquery version; vs
The latter nested ROW constructor version with the aliases removed so it executes
Because CTEs are optimisation fences, rephrasing the nested subquery version to use chained CTEs (WITH expressions) may not perform as well, and won't result in the same plan. In this case you're kind of stuck with ugly nested subqueries until we get some improvements to row_to_json or a way to override the column names in a ROW constructor more directly.
Anyway, in general, the principle is that where you want to create a json object with columns a, b, c, and you wish you could just write the illegal syntax:
ROW(a, b, c) AS outername(name1, name2, name3)
you can instead use scalar subqueries returning row-typed values:
(SELECT x FROM (SELECT a AS name1, b AS name2, c AS name3) x) AS outername
Or:
(SELECT x FROM (SELECT a, b, c) AS x(name1, name2, name3)) AS outername
Additionally, keep in mind that you can compose json values without additional quoting, e.g. if you put the output of a json_agg within a row_to_json, the inner json_agg result won't get quoted as a string, it'll be incorporated directly as json.
e.g. in the arbitrary example:
SELECT row_to_json(
(SELECT x FROM (SELECT
1 AS k1,
2 AS k2,
(SELECT json_agg( (SELECT x FROM (SELECT 1 AS a, 2 AS b) x) )
FROM generate_series(1,2) ) AS k3
) x),
true
);
the output is:
{"k1":1,
"k2":2,
"k3":[{"a":1,"b":2},
{"a":1,"b":2}]}
Note that the json_agg product, [{"a":1,"b":2}, {"a":1,"b":2}], hasn't been escaped again, as text would be.
This means you can compose json operations to construct rows, you don't always have to create hugely complex PostgreSQL composite types then call row_to_json on the output.
I am adding this solution becasue the accepted response does not contemplate N:N relationships. aka: collections of collections of objects
If you have N:N relationships the clausula with it's your friend.
In my example, I would like to build a tree view of the following hierarchy.
A Requirement - Has - TestSuites
A Test Suite - Contains - TestCases.
The following query represents the joins.
SELECT reqId ,r.description as reqDesc ,array_agg(s.id)
s.id as suiteId , s."Name" as suiteName,
tc.id as tcId , tc."Title" as testCaseTitle
from "Requirement" r
inner join "Has" h on r.id = h.requirementid
inner join "TestSuite" s on s.id = h.testsuiteid
inner join "Contains" c on c.testsuiteid = s.id
inner join "TestCase" tc on tc.id = c.testcaseid
GROUP BY r.id, s.id;
Since you can not do multiple aggregations, you need to use "WITH".
with testcases as (
select c.testsuiteid,ts."Name" , tc.id, tc."Title" from "TestSuite" ts
inner join "Contains" c on c.testsuiteid = ts.id
inner join "TestCase" tc on tc.id = c.testcaseid
),
requirements as (
select r.id as reqId ,r.description as reqDesc , s.id as suiteId
from "Requirement" r
inner join "Has" h on r.id = h.requirementid
inner join "TestSuite" s on s.id = h.testsuiteid
)
, suitesJson as (
select testcases.testsuiteid,
json_agg(
json_build_object('tc_id', testcases.id,'tc_title', testcases."Title" )
) as suiteJson
from testcases
group by testcases.testsuiteid,testcases."Name"
),
allSuites as (
select has.requirementid,
json_agg(
json_build_object('ts_id', suitesJson.testsuiteid,'name',s."Name" , 'test_cases', suitesJson.suiteJson )
) as suites
from suitesJson inner join "TestSuite" s on s.id = suitesJson.testsuiteid
inner join "Has" has on has.testsuiteid = s.id
group by has.requirementid
),
allRequirements as (
select json_agg(
json_build_object('req_id', r.id ,'req_description',r.description , 'test_suites', allSuites.suites )
) as suites
from allSuites inner join "Requirement" r on r.id = allSuites.requirementid
)
select * from allRequirements
What it does is building the JSON object in small collection of items and aggregating them on each with clausules.
Result:
[
{
"req_id": 1,
"req_description": "<character varying>",
"test_suites": [
{
"ts_id": 1,
"name": "TestSuite",
"test_cases": [
{
"tc_id": 1,
"tc_title": "TestCase"
},
{
"tc_id": 2,
"tc_title": "TestCase2"
}
]
},
{
"ts_id": 2,
"name": "TestSuite",
"test_cases": [
{
"tc_id": 2,
"tc_title": "TestCase2"
}
]
}
]
},
{
"req_id": 2,
"req_description": "<character varying> 2 ",
"test_suites": [
{
"ts_id": 2,
"name": "TestSuite",
"test_cases": [
{
"tc_id": 2,
"tc_title": "TestCase2"
}
]
}
]
}
]
My suggestion for maintainability over the long term is to use a VIEW to build the coarse version of your query, and then use a function as below:
CREATE OR REPLACE FUNCTION fnc_query_prominence_users( )
RETURNS json AS $$
DECLARE
d_result json;
BEGIN
SELECT ARRAY_TO_JSON(
ARRAY_AGG(
ROW_TO_JSON(
CAST(ROW(users.*) AS prominence.users)
)
)
)
INTO d_result
FROM prominence.users;
RETURN d_result;
END; $$
LANGUAGE plpgsql
SECURITY INVOKER;
In this case, the object prominence.users is a view. Since I selected users.*, I will not have to update this function if I need to update the view to include more fields in a user record.