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Editorial Team
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Asked: 2026-06-19T00:59:55+00:00

When debugging someone code I found that one of the queries was causing the

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When debugging someone code I found that one of the queries was causing the temp table of mysql to run out of memory. I found that the query was executing even though the ‘ON’ condition did not have an equals to match the fields. I was wondering…

What this would actually do as this seemed to cause a horrendous performance lag?

(I ran the explain command which didn’t seem to help)

As a very rudimentary example it would look something like this query:

"SELECT testfield
FROM foo f
LEFT JOIN bar b ON b.testid 
WHERE testid = 40365";
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1 Answer

  1. Editorial Team

    this is because you’re joining on condition TRUE, which means this operation is a bit like a cartesian product.

    I guess your tables are big enough to cause this memory problem.

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