How to group multiple values to only two groups? - sql

Question

So, I have 2 tables.
Type table
id
Name
1.
General
2.
Mostly Used
3.
Low
Component table
id
Name
typeId
1.
Component 1
1
2.
Component 2
1
4.
Component 4
2
6.
Component 6
2
7.
Component 5
3
There can be numerous types but I want to get only 'General' and 'Others' as types along with the component as follows:
[{
"General": [{
"id": "1",
"name": "General",
"component": [{
"id": 1,
"name": "component 1",
"componentTypeId": 1
}, {
"id": 2,
"name": "component 2",
"componentTypeId": 1
}]
}],
"Others": [{
"id": "2",
"name": "Mostly Used",
"component": [{
"id": 4,
"name": "component 4",
"componentTypeId": 2
}, {
"id": 6,
"name": "component 6",
"componentTypeId": 2
}]
},
{
"id": "3",
"name": "Low",
"component": [{
"id": 7,
"name": "component 5",
"componentTypeId": 3
}]
}
]
}]
WITH CTE_TYPES AS (
SELECT
CASE WHEN t. "name" <> 'General' THEN
'Others'
ELSE
'General'
END AS TYPE,
t.id,
t.name
FROM
type AS t
GROUP BY
TYPE,
t.id
),
CTE_COMPONENT AS (
SELECT
c.id,
c.name,
c.typeid
FROM
component c
)
SELECT
JSON_AGG(jsonb_build_object ('id', CT.id, 'name', CT.name, 'type', CT.type, 'component', CC))
FROM
CTE_COMPONENTTYPES CT
INNER JOIN CTE_COMPONENT CC ON CT.id = CC.tradingplancomponenttypeid
GROUP BY
CT.type
I get 2 types from the query as I expected but the components are not grouped together
Can you also point to resources to learn advanced SQL queries?

Answer 1

Here after is a solution to get your expected result as specified in your question :
First part
The first part of the query aggregates all the components with the same TypeId into a jsonb array. It also calculates the new type column with the value 'Others' for all the type names different from General or with the value 'General' :
SELECT CASE WHEN t.name <> 'General' THEN 'Others' ELSE 'General' END AS type
, t.id, t.name
, jsonb_build_object('id', t.id, 'name', t.name, 'component', jsonb_agg(jsonb_build_object('id', c.id, 'name', c.name, 'componentTypeId', c.typeid))) AS list
FROM component AS c
INNER JOIN type AS t
ON t.id = c.typeid
GROUP BY t.id, t.name
jsonb_build_object builds a jsonb object from a set of key/value arguments
jsonb_agg aggregates jsonb objects into a single jsonb array.
Second part
The second part of the query is much more complex because of the structure of your expected result where you want to nest the types which are different from General with their components inside each other according to the TypeId order, ie Low type with TypeId = 3 is nested inside Mostly Used type with TypeId = 2 :
{ "id": "2",
, "name": "Mostly Used"
, "component": [ { "id": 4
, "name": "component 4"
, "componentTypeId": 2
}
, { ... }
, { "id": "3"
, "name": "Low" --> 'Low' type is nested inside 'Mostly Used' type
, "component": [ { "id": 7
, "name": "component 5"
, "componentTypeId": 3
}
, { ... }
]
}
]
}
To do such a nested structure with a random number of TypeId, you could create a recursive query, but I prefer here to create a user-defined aggregate function which will make the query much more simple and readable, see the manual. The aggregate function jsonb_set_inv_agg is based on the user-defined function jsonb_set_inv which inserts the jsonb object x inside the existing jsonb object z according to the path p. This function is based on the jsonb_set standard function :
CREATE OR REPLACE FUNCTION jsonb_set_inv(x jsonb, p text[], z jsonb, b boolean)
RETURNS jsonb LANGUAGE sql IMMUTABLE AS
$$
SELECT jsonb_set(z, p, COALESCE(z#>p || x, z#>p), b) ;
$$ ;
CREATE AGGREGATE jsonb_set_inv_agg(p text[], z jsonb, b boolean)
( sfunc = jsonb_set_inv
, stype = jsonb
) ;
Based on the newly created aggregate function jsonb_set_inv_agg and the jsonb_agg and jsonb_build_object standard functions already seen above, the final query is :
SELECT jsonb_agg(jsonb_build_object('General', x.list)) FILTER (WHERE x.type = 'General')
|| jsonb_build_object('Others', jsonb_set_inv_agg('{component}', x.list, true ORDER BY x.id DESC) FILTER (WHERE x.type = 'Others'))
FROM
( SELECT CASE WHEN t.name <> 'General' THEN 'Others' ELSE 'General' END AS type
, t.id, t.name
, jsonb_build_object('id', t.id, 'name', t.name, 'component', jsonb_agg(jsonb_build_object('id', c.id, 'name', c.name, 'componentTypeId', c.typeid))) AS list
FROM component AS c
INNER JOIN type AS t
ON t.id = c.typeid
GROUP BY t.id, t.name
) AS x
see the full test result in dbfiddle.