Postgresql - Having trouble performing left joins on multiple tables

Question

I'm in the process of moving some Mysql queries over to Postgresql and I ran across this one that doesn't work.

select (tons of stuff)
from trip_publication 

left join trip_collection AS "tc" on
tc.id = tp.collection_id

left join 
            trip_author ta1, (dies here)
            trip_person tp1,
            trip_institution tai1,
            trip_location tail1,
            trip_rank tr1
    ON
            tp.id = ta1.publication_id 
            AND tp1.id = ta1.person_id 
            AND ta1.order = 1 
            AND tai1.id = ta1.institution_id 
            AND tail1.id = tai1.location_id 
            AND ta1.rank_id = tr1.id

The query seems to be dying on the "trip_author ta1" line, where I marked it above. The actual error message is:

   syntax error at or near ","
   LINE 77:   (trip_author ta1, trip_person tp1, ... 

I went through the docs, and it seems to be correct. What exactly am I doing wrong here? Any feedback would be much appreciated.

Answer 1

I don't know postgres, but in regular SQL you would need to a series of LEFT JOIN statements rather than your comma syntax. You seemed to have started this then stopped after the first two.

Something like:

SELECT * FROM
table1 
LEFT JOIN table2 ON match1
LEFT JOIN table3 ON match2
WHERE otherFilters

The alternative is the older SQL syntax of:

SELECT cols
FROM table1, table2, table3
WHERE match AND match2 AND otherFilters

There's a couple of other smaller errors in your SQL, like the fact you forgot your tp alias on your first table, and have tried including a where clause (ta1.order = 1) as a joining constraint.

I think this is what you are after:

select (tons of stuff)
from trip_publication tp 
left join trip_collection AS "tc" on tc.id = tp.collection_id
left join trip_author ta1 on ta1.publication_id  = tp.id
left join trip_person tp1 on tp1.id = ta1.person_id 
left join trip_institution tai1 on  tai1.id = ta1.institution_id 
left join trip_location tail1 on tail1.id = tai1.location_id 
left join trip_rank tr1 on tr1.id = ta1.rank_id
where ta1.order = 1

Answer 2

Your left joins are one per table you are joining

left join trip_author ta1 on ....
left join trip_person tp1 on ....
left join trip_institution on ...

...and so on