This is probably well known issue for everyone having some MySQL experience or experience with any other SQL database. Still I see this problem in many production applications so it is worth to mention it, especially as it is connected to MySQL Performance. No it might not affect MySQL Performance per say but it […]
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MySQL has useful extention to the GROUP BY operation: function GROUP_CONCAT:
GROUP_CONCAT(expr) – This function returns a string result with the concatenated non-NULL values from a group.
Where it can be useful?
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Suboptimal MySQL ORDER BY implementation, especially together with LIMIT is often the cause of MySQL performance problems. Here is what you need to know about MySQL ORDER BY LIMIT optimization to avoid these problems.
MySQL ORDER BY with LIMIT is the most common use of ORDER BY in interactive applications with large data sets being sorted. […]
Starting MySQL 4.1, MySQL had support for what is called derived tables, inline views or basically subselects in the from clause.
In MySQL 5.0 support for views was added.
These features are quite related to each other but how do they compare in terms of performance ?
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Few days ago I wrote an article about using UNION to implement loose index scan.
First I should mention double IN also works same way so you do not have to use the union. So changing query to:
Shell
mysql> SELECT sql_no_cache name FROM people WHERE age in(18,19,20) AND zip IN (12345,12346, 12347);
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