Question

I am using a select statement with a join to try and insert a column into a mySQL database table.

My code:

insert into trips_last_arrival_time(start_time)
select min_arrival_time.start_time
from min_arrival_time 
            inner join trips_last_arrival_time 
            on min_arrival_time.trip_id = trips_last_arrival_time.trip_id;

I am getting :

[Err] 1364 - Field 'trip_id' doesn't have a default value
trip_id is the primary key of both tables. 

The start_time column is blank, not filled with nulls.

I’ve tried an UPDATE clause too

update trips_last_arrival_time
set trips_last_arrival_time.start_time  = (
select start_time from min_arrival_time )
where exists(
select trip_id from trips_last_arrival_time
where trips_last_arrival_time.trip_id = min_arrival_time.trip_id)

And there’s a column trip_id in the table min_arrival_time (in fact it’s the primary key of both tables!)
But this UPDATE clause gives me:

[Err] 1054 - Unknown column 'min_arrival_time.trip_id' in 'where clause'

What am I missing?

Answer 1

You are trying to insert on an existing row (it exists because you have tried to SELECT it). Regardless of whether trip_id has a default value, this is not the correct operation. You need to do an UPDATE.

For your update, I’m pretty sure you need to do this:

UPDATE trips_last_arrival_time AS t, min_arrival_time AS m
    SET t.start_time = m.start_time
    WHERE t.trip_id = m.trip_id;