Does Indexing Boolean Fields Actually Speed Up Queries?

Does Indexing Boolean Fields Improve Performance?

When constructing a query that involves a boolean field comparison, it's common to wonder if indexing the field would yield any performance benefits. Let's delve into this topic to understand the impact of indexing boolean fields.

Consideration of Index Size and Query Simplicity

Contrary to popular belief, indexing boolean fields can indeed improve performance, especially if the field values are skewed. For instance, if a boolean field has a lot of false or zero values, indexing it can help the database engine quickly eliminate non-matching rows, leading to more efficient query execution.

Additionally, indexed fields enable the use of index-only scans, which can be vastly faster than performing full table scans. When the indexed boolean field serves as the sole filter in a query, the database engine can use the index to return the necessary data without having to access the table itself.

Empirical Evidence of Performance Gain

An experienced database engineer shares their experience with indexing a boolean field. In their case, a table with 4 million rows, where only a few thousand rows had a specific boolean flag set, yielded significant performance improvements after indexing the boolean field. The query execution time was reduced from over 9 seconds to a mere fraction of a second.

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