Question

I have 2 tables in MYSQL that will be joined by a foreign key. Each table has its own date field. What I would like to do is combine these two date fields together and then order by the combined information. I understand that you can order by multiple fields but I don’t think that combines them.

Example

Join by tickets.ticket_id = ticket_history.ticket_id

Table 1

ticket_date

Table 2

ticket_history_date

Goal combine the two date fields and then order the rows by the combined dates

Answer 1

Let’s assume that you want the latest of the two dates, you can do something like this

SELECT
    [some info],
    GREATEST( ticket_date, ticket_history_date ) as latest_date
FROM
    [tables and join]
ORDER BY
    latest_date

If you wanted the oldest date you could use LEAST rather than GREATEST. If one of the dates might be NULL then you might want to look into COALESCE