MySQL Select only one row from each patient diagnosed according the first date

Question

EDIT

I cannot group by only with patient_id, I will get an error of sql_mode=only_full_group_by...

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Answer 1

Solution 1: Change database to something using Window Functions, as apparently MySQL has big drawbacks on this field (for example). This could save your day

Solution 2: As probably the first solution won't be acceptable for you, you may try to use something like

    select t1.patient_id, min(t3.date_of_visit) "date_of_visit" 
    from consultation t1 
    LEFT JOIN visit t3 ON t3.visit_id = t1.visit_id
    group by t1.patient_id

You could join this as subquery or put it into some table (maybe even temporary). Join should be done by patient and date_of_visit then.

Unfortunatelly until you provide MCVE like Strawberry requests to, it will be hard to help more.