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?
Share
Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
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?
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