Union Three or more tables with conditions - sql

Question

I need a help to solve some problem.
I have some table levelAsignment with columns level_id, store_id and user_id. For each user_id I can write a query to get his level_ids and store_ids.
Also I have a table stores.
I need to get for each store his level and count the users of the current level and store.
It's easy, but the problem is in storing data, Because in the levelAsignment table the user can set all stores for some operator level.
It looks like this:
level_id | store_Id | user_id
4 1 5
1 5 5
6 1
when store_id = 1 in the stores table it means all stores, so I need to show all stores except 1.
select * from stores where id != 1;
so I need an advice how to organize that.
I find different ways to solve the problem, but there were many unions and conditions.

Answer 1

This depends on how you are able to join the stores table
I think you should join level_assignment (where the store_id = 1) with all data in the stores table, but subquery where the outer query excludes the store_id = 1 column from the level assignment table. You may have to create a join column in temporary tables for the stores data. Then union the level_assignment table where store_id != 1
Example:
WITH get_all_stores_for_store_id_1 AS (
SELECT
a.level_assigment,
a.store_id,
b.store_id,
a.user_id
FROM level_assignment a
LEFT JOIN stores b ON a.join_column = b.join_column
WHERE a.store_id = 1)
SELECT
level_assignment,
b.store_id AS store_id,
user_id
FROM get_all_stores_for_store_id_1
UNION
SELECT
level_assignment,
store_id,
user_id
FROM level_assignment
WHERE store_id != 1
Does that make sense?
Thinking about how to join the data, we could do something like this:
Get the stores table and create a 1 column with a one in every row for the stores, so that we can then join all stores to the level_assignment table with store_id = 1:
WITH set_1_column_in_stores_table AS (
SELECT
1 AS join_id,
store_id,
FROM stores),
all_store_rows_get_all_stores AS (
SELECT
a.level_assigment,
a.store_id,
b.store_id,
a.user_id
FROM level_assignment a
LEFT JOIN set_1_column_in_stores_table b ON a.store_id= b.join_id
-- The above will join all stores where store_id = 1 in level_assigment
WHERE a.store_id = 1)
SELECT
level_assignment,
b.store_id AS store_id,
user_id
FROM all_store_rows_get_all_stores
UNION
SELECT
level_assignment,
store_id,
user_id
FROM level_assignment
WHERE store_id != 1