Why might an engine fall back to heap lookups even if all projected columns are in the index?

Problem Statement

Explanation

Some engines need to confirm row visibility (e.g., via visibility maps) before serving from the index alone. If visibility info is not set, they probe the base table. Regular vacuuming and recent access can improve index-only scans.

Code Solution

SolutionRead Only

-- Postgres example: VACUUM ANALYZE helps visibility maps

Practice Sets

This question appears in the following practice sets:

Indexing Strategies & Access Paths

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Why might an engine fall back to heap lookups even if all projected columns are in the index?

Problem Statement

Explanation

Code Solution

Practice Sets

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Why might an engine fall back to heap lookups even if all projected columns are in the index?

Problem Statement

Explanation

Code Solution

Practice Sets

Related Questions

Which SQL statement retrieves all columns and rows from a table named employees?

Which clause filters rows before aggregation and affects which rows are grouped?

What is the default sort order when ORDER BY is used without ASC or DESC?

Which construct is commonly used to paginate results in SQL engines like Postgres and MySQL?

Which predicate correctly checks for missing values in standard SQL?

More from SQL & Databases

Master Interviews
Anywhere, Anytime