Concatenate column by condition (oracle) - sql

Question

source_id
source_groupid
source_nm
category_id
level_id
12345
34
ABC
7
2
67549
GI
5
1
24751
BL
6
Result
{"id": 12345, "groupid": 34, "name": ABC, "category_id": 7, "level_id": 2}
{"id": 67549, "groupid": , "name": GI, "category_id": 5, "level_id": 1}
SELECT CONCAT ('{','"id": ', source_id,', ', '"groupid": ', source_groupid,', ','"name": ',source_nm,', ','"category_id": ',category_id,', ', '"level_id": ', level_id, '}') as full_info
FROM table
I need to do column concatenation according to the following pattern. If, for example, there is no entry in the group_id or category_id, then how to write the code so that the template changes and looks for lines 2 and 3 as follows.
{"id": 12345, "groupid": 34, "name": ABC, "category_id": 7, "level_id": 2}
{"id": 67549, "name": GI, "category_id": 5, "level_id": 1}
{"id": 24751, "name": BL, "level_id": 6}

Answer 1

Well, in Oracle (which tag you've used), CONCAT function accepts only two arguments, and - therefore - that code won't work.
Instead, use a double pipe || operator. As of your main problem, CASE it is.
SQL> with test (source_id, source_groupid, source_nm, category_id, level_id) as
2 (select 12345, 34, 'ABC', 7, 2 from dual union all
3 select 67549, null, 'GI' , 5, 1 from dual union all
4 select 24751, null, 'BL' , null, 6 from dual
5 )
6 select '{' || '"id": ' || source_id ||
7 case when source_groupid is not null then ', "groupid": ' || source_groupid end ||
8 case when source_nm is not null then ', "name": ' || source_nm end ||
9 case when category_id is not null then ', "category_id": ' || category_id end ||
10 case when level_id is not null then ', "level_id": ' || level_id end || '}'
11 as result
12 from test;
RESULT
--------------------------------------------------------------------------------
{"id": 12345, "groupid": 34, "name": ABC, "category_id": 7, "level_id": 2}
{"id": 67549, "name": GI, "category_id": 5, "level_id": 1}
{"id": 24751, "name": BL, "level_id": 6}
SQL>

Answer 2

From Oracle 12, don't build JSON by hand; use the JSON_OBJECT function and then you can use ABSENT ON NULL:
SELECT JSON_OBJECT(
KEY 'id' VALUE source_id,
KEY 'groupid' VALUE source_groupid,
KEY 'name' VALUE source_nm,
KEY 'category_id' VALUE category_id,
KEY 'level_id' VALUE level_id
ABSENT ON NULL
) As json
FROM table_name;
Which, for the sample data:
CREATE TABLE table_name (source_id, source_groupid, source_nm, category_id, level_id) AS
SELECT 12345, 34, 'ABC', 7, 2 FROM DUAL UNION ALL
SELECT 67549, NULL, 'GI', 5, 1 FROM DUAL UNION ALL
SELECT 24751, NULL, 'BL', NULL, 6 FROM DUAL;
Outputs:
JSON
{"id":12345,"groupid":34,"name":"ABC","category_id":7,"level_id":2}
{"id":67549,"name":"GI","category_id":5,"level_id":1}
{"id":24751,"name":"BL","level_id":6}
db<>fiddle here