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Choosing the appropriate index for a database is essential for optimizing query performance. Index selectivity is a key factor in determining the effectiveness of an index. This article explains how to analyze index selectivity and select the right index for your database.
Understanding Index Selectivity
Index selectivity measures how well an index distinguishes between different rows in a table. It is calculated by dividing the number of unique values in a column by the total number of rows. High selectivity indicates that the index can efficiently filter data, improving query speed.
How to Analyze Index Selectivity
To analyze index selectivity, examine the distribution of data within the column you plan to index. Use database tools or queries to determine the number of distinct values and compare it to the total row count. Columns with many unique values tend to have higher selectivity.
Choosing the Right Index
When selecting an index, prioritize columns with high selectivity for equality searches. For columns with low selectivity, such as boolean flags or status indicators, a different indexing strategy may be more effective. Combining multiple columns into a composite index can also improve performance for complex queries.
- High selectivity columns
- Columns used frequently in WHERE clauses
- Columns with unique or nearly unique values
- Consider composite indexes for multi-column queries