When `OR` Disables Index — Rewrite With UNION

Problem

`SELECT * FROM users WHERE email = ? OR phone = ?` may table-scan even when both columns are indexed. Why, and how does UNION ALL fix it?

Input

Conceptual + SQL.

Output

Rewritten query

Constraints

—

Sample input

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Sample output

OR predicates across different indexed columns force the planner to choose one or scan; UNION ALL of two index seeks beats it.

Explanation

OR can defeat index intersection; UNION ALL is two cheap seeks.

optimisationor-vs-union@DoorDash

Visible test cases

in: explain

out: ok

Your solution — run it, use AI if stuck

sql