What is an Execution Plan?
An execution plan shows how SQL Server executes a query and retrieves the requested data.
It displays operations such as:
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Table scan or index scan
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Index seek
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Joins
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Sorting and filtering
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Key lookups
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Estimated number of rows
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Cost of each operation
Types
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Estimated Execution Plan: Shows the expected execution method without running the query.
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Actual Execution Plan: Runs the query and includes real execution details, such as actual rows processed.
Why is it useful?
It helps identify performance problems such as:
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Full-table scans
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Missing or inefficient indexes
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Expensive joins and key lookups
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Incorrect row estimates
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Sort or hash spills
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Implicit conversions
Example
SELECT *
FROM Employees
WHERE DepartmentId = 10;The plan may show an Index Seek if a suitable index exists, or a Table Scan if it does not.
Key point
An execution plan is the primary tool for understanding and troubleshooting SQL query performance. Always examine the actual execution plan when possible.