When show index in a table, there are two parts Collation and Cardinality which I don't understand what there usage is. Anyone could briefly explain?
1
- dup of What is cardinality in MySQL? PLease explain simple non technical language, What is collation method?. See also Difference between Encoding and collation?outis– outis2012-07-19 00:29:37 +00:00Commented Jul 19, 2012 at 0:29
Add a comment |
1 Answer
Collation is the way sorting takes place, based on the character set you specify. See https://dev.mysql.com/doc/refman/5.5/en/charset-charsets.html
Cardinality is basically "How many unique elements does this column contain." A table with low cardinality has few unique values. Lookup tables generally have much lower cardinality than tables of a particular entity such as Customers.
http://en.wikipedia.org/wiki/Cardinality_%28SQL_statements%29
