When can rewriting a wide OR predicate as UNION ALL improve performance?

Problem Statement

Explanation

Wide ORs often disable index seeks. Splitting into separate queries lets each branch use the best index, then UNION ALL combines results. Add DISTINCT only if needed, since it adds sort or hash work. Ensure predicates are mutually exclusive or dedupe explicitly.

Code Solution

SolutionRead Only

(SELECT * FROM users WHERE email = $1)
UNION ALL
(SELECT * FROM users WHERE phone = $2)

Practice Sets

This question appears in the following practice sets:

Query Optimization & Execution Plans

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When can rewriting a wide OR predicate as UNION ALL improve performance?

Problem Statement

Explanation

Code Solution

Practice Sets

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Master Interviews Anywhere, Anytime

When can rewriting a wide OR predicate as UNION ALL improve performance?

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