Slow Left Join on 100K row tables
Posted by: Biju Philips
Date: March 09, 2022 08:58PM

I have an issue with Left Join being extremely slow between two tables with 100K rows each. I am tracking changes use MD5 hash keys. Each table has only 2 fields the key (GUID) and the HashKey. Inner Join and Left Join from b to a is working but Left Join from a to b is not working. Both tables have index on the Key field. What else can I do to get this to work? This is part of a large replication project I am working on so should be something I can automate on all tables in the database. Below is the query MySQL used.

select count(1)
From Table1 a
Left Join Table2 b
On a.Id = b.Id
Where b.Id Is Null;

Version: 5.7.36-39-log Innodb.

Thanks!

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Slow Left Join on 100K row tables
March 09, 2022 08:58PM


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