Select 条件取决于另一列的值的语句 - 同一个表（mysql）

Question

I have table with 3 columns:

ID, 
Cancellation_Policy_Type 
Cancellation_Policy_Hours.

The query I would like to get to will allow me to select:

• the min Cancellation_Policy_Hours which correspond to the Free Cancellation (if exists)
• if the above doesn't exist for the specific ID, then I want to check if there is a partially refundable
• if none of the above exist, then check if there is No Refundable.

The below query is not correct but it may give a better idea about what I am trying to achieve:

IF (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Free Cancellation') IS NOT NULL)
THEN (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Free Cancellation')
ELSEIF (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Free Cancellation') IS NULL AND (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours  from MYTABLE WHERE Cancellation_Policy_Type = 'Partially Refundable') IS NOT NULL Then (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Partially Refundable')
ELSEIF (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Free Cancellation') IS NULL AND (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'Partially Refundable') IS NULL  THEN (SELECT ID, Cancellation_Policy_Type, MIN(Cancellation_Policy_Hours) from MYTABLE WHERE Cancellation_Policy_Type = 'No Refundable') 
END

Below you will find an example of my dataset:

This is the table which contains all data regarding the cancellation policies of every single ID:

ID	Cancellation_Policy_Type	Cancellation_Policy_Hours
1	No Refundable	17520
1	Partially Refunable	168
1	Free Cancellation	96
2	No Refundable	17520
2	Partially Refunable	336
2	Free Cancellation	48
3	No Refundable	17520
3	Partially Refunable	336
4	No Refundable	17520

Below is the desired result, that is a table which contains other pieces of information (including production) and the 2 columns where for every single ID repeats the best available cancellation policy type and hours:

ID	Most Flexible Cancellation Type	Most Flexible Cancellation Hours	Other Columns (including buckets)
1	Free Cancellation	96	a
1	Free Cancellation	96	b
1	Free Cancellation	96	c
2	Free Cancellation	48	a
2	Free Cancellation	48	b
2	Free Cancellation	48	c
3	Partially Refunable	336	a
3	Partially Refunable	336	b
3	Partially Refunable	336	c
4	No Refundable	17520	a
4	No Refundable	17520	b
4	No Refundable	17520	c

SELECT
a.ID
, Most_Flexible_Policy_Type 
, Most_Flexible_Cancellation_Hours
, a.BookingWindowBuckets
FROM Production a
LEFT JOIN Property b on a.ID = b.ID
GROUP BY
1,2,3,4

Thank you

Answer 1

I understand that, for each row in production , you want to bring from table property the cancellation policy with the least policy hours.

We can do this with window functions to rank the policies of feach id , and a join to production :

select d.id, 
    p.cancellation_type_policy  most_flexible_cancellation_type,
    p.cancellation_policy_hours most_flexible_cancellation_hours
from production d
inner join (
    select p.*, row_number() over(partition by id order by cancellation_policy_hours) rn
    from property p
) p on p.id = d.id
where rn = 1

Answer 2

You have not given enough information to be able to help you with any degree of confidence that it is the "right" way but (guessing here) you could try -

SELECT
    ID,
    MIN(IF(Cancellation_Policy_Type = 'Free Cancellation', Cancellation_Policy_Hours, NULL)) AS minFreeCancellation,
    MIN(IF(Cancellation_Policy_Type = 'Partially Refundable', Cancellation_Policy_Hours, NULL)) AS minPartiallyRefundable,
    MIN(IF(Cancellation_Policy_Type = 'No Refundable', Cancellation_Policy_Hours, NULL)) AS minNoRefundable
FROM MYTABLE
WHERE ID = ?
GROUP BY ID;

If you provide an example in the form of full table structure (CREATE statement), some sample data, some stats and the desired outcome you are more likely to get the "right" answer. The above example of conditional aggregation is unlikely to be the best way to do it but it will probably provide what you are looking for. Depending on your dataset, just running the separate queries may be the best solution.

UPDATE Here is one way of doing this using a window function (MySQL 8) -

WITH Properties (ID, Cancellation_Policy_Type, Cancellation_Policy_Hours, Most_Flexible) AS (
    SELECT
        ID, Cancellation_Policy_Type, Cancellation_Policy_Hours,
        ROW_NUMBER() OVER (PARTITION BY ID ORDER BY
            CASE Cancellation_Policy_Type
                WHEN 'Free Cancellation' THEN 0
                WHEN 'Partially Refundable' THEN 1
                WHEN 'No Refundable' THEN 2
            END ASC, Cancellation_Policy_Hours ASC
        )
    FROM Property
)
SELECT
    a.ID,
    b.Cancellation_Policy_Type,
    b.Cancellation_Policy_Hours,
    a.BookingWindowBuckets
FROM Production a
LEFT JOIN Properties b on a.ID = b.ID
WHERE b.Most_Flexible = 1;