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Displaying posts with tag: not exists (reset)
SQL EXISTS and NOT EXISTS

Introduction In this article, we are going to see how the SQL EXISTS operator works and when you should use it. Although the EXISTS operator has been available since SQL:86, the very first edition of the SQL Standard, I found that there are still many application developers who don’t realize how powerful SQL subquery expressions really are when it comes to filtering a given table based on a condition evaluated on a different table. Database table model Let’s assume we have the following two tables in our database, that form a one-to-many... Read More

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NOT IN vs. NOT EXISTS vs. LEFT JOIN / IS NULL: MySQL

When you’re spoiled with Oracle’s fabulous query transformation capabilities and its really well-done cost-based optimiser, then you might forget how difficult SQL query tuning used to be in the “old days” or with those less sophisticated databases. Here’s a really nice explanation of the various means of implementing an ANTI-JOIN in MySQL:

http://explainextended.com/2009/09/18/not-in-vs-not-exists-vs-left-join-is-null-mysql/

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