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Data & Analytics · Intermediate

Query Execution Plan

The sequence of physical operations (scans, seeks, joins, sorts) that the database chooses to run a query.

Definition

Execution plans show estimated or actual costs, row counts and operator choices. Analysts read them to find full scans, missing indexes, poor join choices, spills and cardinality misestimates. Tools include EXPLAIN in PostgreSQL, MySQL and Snowflake, SSMS graphical plans and the Snowflake Query Profile.

Example

EXPLAIN SELECT * FROM orders WHERE customer_id = 42;

Exam tip

A large gap between estimated and actual rows usually points to stale statistics.

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