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Asked: 2026-06-16T01:21:30+00:00

I’m getting duplicates when I do two LEFT JOINs to get to the event_name

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I’m getting duplicates when I do two LEFT JOINs to get to the “event_name” in my example below. I get 112 cases with it set up this way. However, if I get rid of the 2 LEFT JOIN lines and run the query, I get the proper 100 records without duplicates. I tried DISTINCT with the code below, but I still get 112 with duplicates.

SELECT "cases"."id", "cases"."date", "cases"."name", "event"."event_name" 
FROM "cases"
LEFT JOIN "middle_table" ON "cases"."serial" = "middle_table"."m_serial"
LEFT JOIN "event" ON "middle_table"."e_serial" = "event"."ev_serial"
WHERE "cases"."date" BETWEEN '2012-12-11' AND '2012-12-13'

How can I specify that I only want the exact 100 cases from “cases”, and that I don’t want anything from the tables in the joins to produce any more rows?

Thanks!

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1 Answer

  1. Editorial Team

    You need to extend your ON clauses to include a condition so that for each entry in cases there is only one entry in middle_table that matches the condition and that for each entry in middle_table there is only one entry in event:

    LEFT JOIN middle_table ON cases.serial = middle_table.m_serial AND some_condition

    You can of course use DISTINCT. If that doesn’t work it means that your results are all different in the fields cases.id, cases.date, cases.name and event.event_name. Examine the results and decide which of the entries you want to throw away and include that condition in your ON clause.

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