How to update a column pertaining to MySQL table with values from another column in another table using inner join?

Question

Event table (initial) :

status table:

table ready_reason:

table delay_reason :

table spare_reason:

table down_reason :

Required output

So basically, I've to replace the values in the columns status code and reason code in the event table with the corresponding values from the tables below.

I tried all sorts of permutation and combinations of inner joins. However, couldn't crack it. Would appreciate any insights.

My code to update status code column (didn't work) :

update event eve
set eve.status_code = sta.name
inner join status sta on eve.status_code = sta.status_code

Since reason_ code column in event table needs to be update using multiple table, I'm unable to come up with code for this one

Answer 1

Instead of updating the names to the code fields you could create a view.

The example below uses LEFT JOIN's on the reason tables, and then COALESCE's the reason names.

CREATE VIEW vwEvent AS
SELECT 
 ev.*, 
 COALESCE(st.Name, ev.`Status Code`) AS `Status Name`, 
 COALESCE(ready.Name, delay.Name, spare.Name, down.Name, ev.`Reason Code`) AS `Reason Name`
FROM `event` ev
LEFT JOIN `status` AS st ON st.`Status Code` = ev.`Status Code`
LEFT JOIN ready_reason AS ready ON (ev.`Status Code` = 'R'  AND ready.`Status Code` = ev.`Reason Code`)
LEFT JOIN delay_reason AS delay ON (ev.`Status Code` = 'D1' AND delay.`Status Code` = ev.`Reason Code`)
LEFT JOIN spare_reason AS spare ON (ev.`Status Code` = 'S'  AND spare.`Status Code` = ev.`Reason Code`)
LEFT JOIN down_reason  AS down  ON (ev.`Status Code` = 'D2' AND down.`Status Code`  = ev.`Reason Code`);

Then select from the view to get the status and reason names:

select EventId, Duration, `Status Name`, `Reason Name`
from vwEvent

Test on db<>fiddle here

Well, I suppose you could use the view to update the table itself.
But that might not be the best idea.

update `event` ev
join `vwEvent` vw on vw.EventId = ev.EventId
set ev.`Status Code` = vw.`Status Name`,
    ev.`Reason Code` = vw.`Reason Name`

Answer 2

Do an update using LEFT JOIN on "reason" tables and COALESCE on the name column from those tables

UPDATE event e 
JOIN status s ON s.status_code = e.status_code
LEFT JOIN ready_reason r ON r.status_code = e.reason_code AND e.status_code = 'R'
LEFT JOIN delay_reason d ON d.status_code = e.reason_code AND e.status_code = 'D1'
LEFT JOIN spare_reason sp ON sp.status_code = e.reason_code 
LEFT JOIN down_reason do ON do.status_code = e.reason_code
SET e.status_code = s.name, e.reason_code = COALESCE(r.name, d.name, sp.name, do.name)

Answer 3

使用连接，例如，我从上面使用了2个表连接，就可以像下面这样用普通列完成所有表连接

SELECT * FROM Event table e LEFT JOIN status s ON e.status_code=s.status_code  

Answer 4

Assuming the values in your tables are static, following code can update base on CASE-WHEN in MySQL.

update event eve
set eve.status_code = (SELECT name from status_table WHERE status_code = eve.status_code), eve.reason_code =   CASE

WHEN eve.status_code = 'R' THEN (SELECT name from ready_reason WHERE status_code = eve.reason_code)

WHEN eve.status_code = 'D1' THEN (SELECT name from delay_reason WHERE status_code = eve.reason_code)

WHEN eve.status_code = 'S' THEN (SELECT name from spare_reason WHERE status_code = eve.reason_code)

WHEN eve.status_code = 'D2' THEN (SELECT name from down_reason WHERE status_code = eve.reason_code)