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1. stackoverflow.com › questions › 2566211indexing - What is cardinality in MySQL? - Stack Overflow

   stackoverflow.com › questions › 2566211

   Apr 2, 2010 · 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.

2. www.mysqltutorial.org › mysql-index-cardinalityMySQL Index Cardinality Explained - MySQL Tutorial

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   MySQL uses index cardinality to optimize database performance and query efficiency. Was this tutorial helpful? This tutorial explains you the MySQL Index Cardinality and shows you how to view the index cardinality information using the SHOW INDEXES command.

3. effectivemysql.com › article › index-cardinalityIndex Cardinality - Effective MySQL

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   Feb 4, 2011 · Index Cardinality refers to the uniqueness of values for a given column within an index. The value can be considered as the number of probable unique values found. Looking at the Primary Key or an Unique Key will provide a representative large number matching approximately (*) to the number of table rows.

4. www.tutorialspoint.com › what-is-cardinality-in-mysqlWhat is cardinality in MySQL? - Online Tutorials Library

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   Jul 30, 2019 · In MySQL, the term cardinality refers to the uniqueness of data values that can be put into columns. It is a kind of property which influences the ability to search, cluster and sort data. Cardinality can be of two types which are as follows −. Low Cardinality − All values for a column must be same.

5. severalnines.com › blog › understanding-indexesUnderstanding Indexes in MySQL: Part Three - Severalnines

   severalnines.com › blog › understanding-indexes

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   May 18, 2021 · In very simple terms, index cardinality refers to the uniqueness of values stored in a column that uses an index. To view the index cardinality of a specific index, you can simply go to the Structure tab of phpMyAdmin and observe the information there or you can also execute a SHOW INDEXES query:

6. www.sqliz.com › mysql › index-cardinalityMySQL index cardinality

   www.sqliz.com › mysql › index-cardinality

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   Index cardinality is an important basis for the MySQL query optimizer to decide whether to use an index. This article discusses the index cardinality of MySQL and how to use the SHOW INDEXES command to view index cardinality.

7. People also ask

   What is cardinality in MySQL?

   • An estimate of the number of unique values in the index. This is updated by running ANALYZE TABLE or myisamchk -a. Cardinality is counted based on statistics stored as integers, so the value is not necessarily exact even for small tables. The higher the cardinality, the greater the chance that MySQL uses the index when doing joins.

   indexing - What is cardinality in MySQL? - Stack Overflow

   stackoverflow.com/questions/2566211/what-is-cardinality-in-mysql

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   What if MySQL chooses an index with Poor cardinality?

   • If MySQL chooses an index with poor cardinality, it may be more effective to scan all data rows sequentially without an index. The SHOW INDEXES command can be used to view the cardinality of indexes. For example: NOTE: This output has been modified for display purposes, some columns have been removed.

   Index Cardinality — Effective MySQL

   effectivemysql.com/article/index-cardinality/

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   What is index cardinality?

   • Index Cardinality refers to the uniqueness of values for a given column within an index. The value can be considered as the number of probable unique values found. Looking at the Primary Key or an Unique Key will provide a representative large number matching approximately (*) to the number of table rows.

   Index Cardinality — Effective MySQL

   effectivemysql.com/article/index-cardinality/

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   What if a column has high cardinality?

   • If a column has high cardinality, it’s likely to be a good candidate for indexing. For example, the following query that retrieves orders from a customer is likely to benefit from the index since the cardinality is relatively high: Index cardinality measures the uniqueness of values in a specific index column.

   MySQL Index Cardinality Explained - MySQL Tutorial

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   How does a query optimizer use index cardinality?

   • The query optimizer uses the index cardinality to generate an optimal query plan for a given query. It also uses index cardinality to decide whether to use the index or not in the join operations. If the query optimizer chooses the index with low cardinality, it may be more effective than scanning rows without using the index.

   MySQL Index Cardinality Explained - MySQL Tutorial

   www.mysqltutorial.org/mysql-index/mysql-index-cardinality/

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   Does index cardinality have a brother?

   • With that being said, index cardinality also has a brother – his name is index selectivity. An index selectivity is the number of distinct values in relation to the number of records in the table. In simple terms, index selectivity defines how tightly a database index helps MySQL narrow the search for values.

   Understanding Indexes in MySQL: Part Three - Severalnines

   severalnines.com/blog/understanding-indexes-mysql-part-three/

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8. www.percona.com › blog › understanding-mysql-indexesUnderstanding MySQL Indexes: Types, Benefits, and Best Practices

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   Sep 23, 2024 · We’ve learned how MySQL indexes work and when certain kinds can be useful, so we’ll now cover some important practices for creating and removing them, monitoring their effectiveness, and dealing with index fragmentation.