how to populate the data from table which unmapped column in join - mysql

Question

I am having below tables and want to populate the PAYID from the PAY table by looking in to CATEGORY_ID for below use case
if PAYID is mapped with CATEGORY_ID then return the PAYID
if PAYID is not mapped to CATEGORY_ID then look for BILL_ID and populate is by joining the NETWORK_CATEGORY and CATEGORY table.
If PAYID is not mapped to CATEGORY_ID and even BILL_ID is not associated with NETWORK_CATEGORY_ID then return the CATEGORY_ID as 3 (Uncategorized) for PAY.
Below is the my tables,
PAY Table
PAYID BILL_ID CATEGORY_ID
101 1 1
102 2
103 3
BILL Table
BILL_ID NAME NETWORK_CATEGORY_ID
1 ABC 42
2 XYZ
3 DSC 23
NETWORK_CATEGORY Table
NETWORK_CATEGORY_ID NAME CATEGORY_ID
42 Electric/gas 1
23 ISP 2
CATEGORIES
CATEGORY_ID NAME
1 Utilities
2 Telecom
3 Uncategorized
And i have written below queries ,
select payid(
select payid from PAY p
where p.CATEGORY_ID in (:categoryIds)
UNION
select payid from PAY p
join BILLS b on p.BILL_ID = b.BILL_ID
where NETWORK_CATEGORY_ID in
(
select NETWORK_CATEGORY_ID
from NETWORK_CATEGORY nc
join CATEGORIES c on nc.CATEGORY_ID = c.CATEGORY_ID
where c.CATEGORY_ID in (:categoryIds)
)
and CATEGORY_ID is null
)
My expectation is that if i passed the categoryIds as 3 or (1,2,3 )then it should return the PAYID as 102 and 101,102,103 respectively.
How can i do that.
Or i can say that how can achieve this task,
If PAYID is not mapped to CATEGORY_ID and even BILL_ID is not associated with NETWORK_CATEGORY_ID then return the CATEGORY_ID as 3 (Uncategorized) for PAY.
By using three union i can achieve that but that not looks an efficient solution.

Answer 1

SELECT p.PAYID
FROM PAY p
WHERE p.CATEGORY_ID IN (2,3)
UNION ALL
SELECT p.PAYID
FROM PAY p
JOIN BILL b
ON p.CATEGORY_ID IS NULL AND p.BILL_ID = b.BILL_ID
JOIN NETWORK_CATEGORY nc
ON b.NETWORK_CATEGORY_ID = nc.NETWORK_CATEGORY_ID
WHERE nc.CATEGORY_ID IN (2,3)
UNION ALL
SELECT p.PAYID
FROM PAY p
LEFT JOIN BILL b
ON p.CATEGORY_ID IS NULL AND p.BILL_ID = b.BILL_ID
LEFT JOIN NETWORK_CATEGORY nc
ON b.NETWORK_CATEGORY_ID = nc.NETWORK_CATEGORY_ID
WHERE (3 IN (2,3) AND p.CATEGORY_ID IS NULL AND nc.CATEGORY_ID IS NULL)
Depending on the size of the dataset and the other criteria being applied to the PAY table, this may perform OK -
SELECT p.PAYID
FROM PAY p
LEFT JOIN BILL b
ON p.CATEGORY_ID IS NULL AND p.BILL_ID = b.BILL_ID
LEFT JOIN NETWORK_CATEGORY nc
ON b.NETWORK_CATEGORY_ID = nc.NETWORK_CATEGORY_ID
WHERE p.CATEGORY_ID IN (2,3)
OR nc.CATEGORY_ID IN (2,3)
OR (3 IN (2,3) AND p.CATEGORY_ID IS NULL AND nc.CATEGORY_ID IS NULL)

Answer 2

Messy but 1) first subquery (x) to cater for no entries, 2) first part of union to check category id, 3) UNION to deal with situation where bill_id and category_id are the same, 4) second part of union to find pay via bill, 5) coalesce to cater for no entries.
select coalesce(payid,3) payid,s.`bill/category id`
from
(select 2 `bill/category id` ) x
left join
(select payid ,category_id as `bill/category id` from pay where category_id = 2
union
select payid ,bill.bill_id
from bill
join network_category nc on bill.network_category_id = nc.network_category_id
join pay on pay.bill_id = nc.category_id
where bill.bill_id = 2
and not exists (select payid from pay where category_id = 2)
) s on s.`bill/category id` = x.`bill/category id`