MySQl中关于Cardinality的理解

Cardinality的定义:In SQL (Structured
Query Language), the term cardinality refers
to the uniqueness of
data values contained in a particular column (attribute) of a database table.
The lower the cardinality, the more duplicated elements in a column. Thus, a column with the lowest possible cardinality would have the same value for every row. SQL databases use cardinality to help determine the optimal query
plan for a given query.

Cardinality的作用:QL
databases use cardinality to help determine the optimal query
plan for a given query.

参考链接:http://dev.mysql.com/doc/refman/5.7/en/show-index.html

               https://en.wikipedia.org/wiki/Cardinality_(SQL_statements)

中文博客:http://blog.csdn.net/lxpbs8851/article/details/8477471