replace NOT IN with LEFT JOIN - sql

Question

I've got a table structure like this
[condition]
condition_id, (pk)
question_id (fk)
[option]
condition_id, (fk)
ext_id (fk)
[external]
ext_id, (pk)
inst_id (fk)
[instance]
inst_id, (pk)
keeper_id (fk)
[keeper]
keeper_id, (pk)
org_id
[question]
question_id (pk)
org_id
[localization]
question_id (fk, pk),
org_id (pk),
language (pk)
label
I need to get all questions from question table with localizations (from localization table), that do not exist in condition table for certain ext_id.
My query is
SELECT
q.question_id as q_id,
l.label as q_value
FROM question q
INNER JOIN localization l
ON l.question_id = q.question_id
INNER JOIN external ex
ON ex.ext_id = 'EXTERNAL_ID'
INNER JOIN instance i
ON i.inst_id = ex.inst_id
INNER JOIN keeper k
ON k.keeper_id = i.keeper_id
WHERE q.org_id IN ('*', k.org_id)
AND l.org_id = '*'
AND l.language = 'EN'
AND q.question_id NOT IN (
SELECT
question_id
FROM condition c
INNER JOIN option o
ON o.condition_id = c.condition_id
WHERE o.ext_id = 'EXTERNAL_ID'
)
But how to replace that subquery with LEFT JOIN?

Answer 1

Here is one way
SELECT p.question_id AS q_id,
l.label AS q_value
FROM question q
INNER JOIN localization l
ON l.question_id = q.question_id
INNER JOIN EXTERNAL ex
ON ex.ext_id = 'EXTERNAL_ID'
INNER JOIN instance i
ON i.inst_id = ex.inst_id
INNER JOIN keeper k
ON k.keeper_id = i.keeper_id
LEFT JOIN (select distinct c.question_id
from condition c
JOIN option o
ON o.condition_id = c.condition_id
AND o.ext_id = 'EXTERNAL_ID' ) c
ON c.question_id = q.question_id
WHERE q.org_id IN ( '*', k.org_id )
AND l.org_id = '*'
AND l.language = 'EN'
AND c.question_id IS NULL
I am not a expert in Postgres but I prefer NOT EXISTS to do this
SELECT p.question_id AS q_id,
l.label AS q_value
FROM question q
INNER JOIN localization l
ON l.question_id = q.question_id
INNER JOIN EXTERNAL ex
ON ex.ext_id = 'EXTERNAL_ID'
INNER JOIN instance i
ON i.inst_id = ex.inst_id
INNER JOIN keeper k
ON k.keeper_id = i.keeper_id
WHERE q.org_id IN ( '*', k.org_id )
AND l.org_id = '*'
AND l.language = 'EN'
AND NOT EXISTS (SELECT 1
FROM condition c
INNER JOIN option o
ON o.condition_id = c.condition_id
WHERE o.ext_id = 'EXTERNAL_ID'
AND q.question_id = c.question_id)