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Displaying posts with tag: query planner (reset)

Query Planner Gotchas
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Indexes can reduce the amount of data your query touches by orders of magnitude. This results in a proportional query speedup. So what happens when you define a nice set of indexes and you don’t get the performance pop you were expecting? Consider the following example:

mysql> show create table t;
| t     | CREATE TABLE `t` (
  `a` varchar(255) DEFAULT NULL,
  `b` bigint(20) NOT NULL DEFAULT '0',
  `c` bigint(20) NOT NULL DEFAULT '0',
  `d` bigint(20) DEFAULT NULL,
  `e` char(255) DEFAULT NULL,
  PRIMARY KEY (`b`,`c`),
  KEY `a` (`a`,`b`,`d`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

Now we’d like to perform the following query:

select sql_no_cache count(d) from t where a = 'this is a test' and b between 8000000 and 8100000;

Great! We have index a, which cover this query. Using a should be really fast. You’d expect to use

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