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Re: Multiple Databases - Search and retrieve.
Posted by: Rick James
Date: July 11, 2011 11:26AM

> SELECT SQL_CALC_FOUND_ROWS name, email FROM users WHERE name LIKE 'a%' LIMIT 10;
> SELECT FOUND_ROWS();
If you have an plain index (I don't mean FULLTEXT) on `name`, that format is more efficient. It will first pick a random 10 rows where name starts with a. Since you are asking for more than just the name, it will hit 10 data rows. The, to get the FOUND_ROWS, it will continue using only then index.

If you do LIKE '%a' (leading wildcard), performance suffers because it will require an index scan.

If you have more than 10K databases, or 10K tables in a single database, or 100M rows in a table, then performance issues increase. 7 is no problem; 70K would be a problem.

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Re: Multiple Databases - Search and retrieve.
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