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What is index cardinality?
For indexes, it is a bit more specialized – cardinality means the number of unique values for the index key. So if the column an index is on has only two values – “yes” and “no”, then the index cardinality is two, no matter how many rows are in the table.
Can you index on datetime?
There’s no problem indexing on datetime. But you shouldn’t add indexes that aren’t necessary for your queries. Adding random indexes doesn’t make anything better, you have to know what the index will be used for. Otherwise it’s just unnecessary overhead.
How do I create an index in SQL Server?
SQL Server CREATE INDEX statement In this syntax: First, specify the name of the index after the CREATE NONCLUSTERED INDEX clause. Note that the NONCLUSTERED keyword is optional. Second, specify the table name on which you want to create the index and a list of columns of that table as the index key columns.
Is it good idea to index datetime field in…?
MySQL recommends using indexes for a variety of reasons including elimination of rows between conditions: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html This makes your datetime column an excellent candidate for an index if you are going to be using it in conditions frequently in queries.
How to use indexed datetime column in MySQL?
MyISAM only uses index caching. Since the query should not touch the .MYD file, you should use a slightly bigger MyISAM Key Buffer. Give it a Try !!! Change your date column type to an integer. Store the date as a Unix date in integer. Timestamp Is a lot larger than an int. You’d get some bang out of that.
Why is indexing date a bad choice in MySQL?
I figured that indexing date will give me “bad” cardinality and thus MySQL won’t use it. http is also a bad choice as there are only about 20 different possible values. Thanks for you help! and used his query, but it performed equally bad.