so when there’s an index on a column, and you do a simple SELECT * FROM table WHERE indexed_column = value, is that a O(1) search? does it matter whether the contents indexed are integers or string?
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so when there’s an index on a column, and you do a simple SELECT * FROM table WHERE indexed_column = value, is that a O(1) search? does it matter whether the contents indexed are integers or string?
None of the lookups in MySQL’s MyISAM or InnoDB storage engines are O(1) searches. Those storage engines use B+Trees to implement indexes. The best they can do is O(log2n) searches.
The
MEMORYstorage engine uses a HASH index type by default, as well as the B+Tree index type. Only the HASH index can achieve O(1) lookups.The data type of the indexed column doesn’t change this in either case.
For more on MySQL indexes, read http://dev.mysql.com/doc/refman/5.1/en/mysql-indexes.html