A selective query uses an index sometimes but scans at other times. How do statistics influence this and how would you fix it?

Problem Statement

Explanation

The optimizer estimates row counts from column and histogram statistics. If stats are stale or too generic, it may think many rows match and pick a scan. Update statistics, increase histogram buckets for skewed columns, or create filtered stats if supported. Also check parameter sniffing and ensure literals or sniffed values reflect common cases. Verify that predicates are SARGable.

Code Solution

SolutionRead Only

-- Postgres
ANALYZE users;
-- SQL Server
UPDATE STATISTICS users WITH FULLSCAN;

Practice Sets

This question appears in the following practice sets:

Indexing Strategies & Access Paths

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A selective query uses an index sometimes but scans at other times. How do statistics influence this and how would you fix it?

Problem Statement

Explanation

Code Solution

Practice Sets

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

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Master Interviews Anywhere, Anytime

A selective query uses an index sometimes but scans at other times. How do statistics influence this and how would you fix it?

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