What is difference between INDEX SEEK vs INDEX SCAN?

Question

Anubhav Sharma · Answer

Understanding how SQL Server reads data is key to performance tuning. Two common operations you’ll see in execution plans are Index Seek and Index Scan.

What is INDEX SEEK?

An Index Seek is a targeted lookup.
SQL Server uses the index to jump directly to matching rows
Very fast and efficient
Works when your query has selective filters

Example:

SELECT * FROM Employees
WHERE Id = 100;

If Id is indexed, SQL Server performs an Index Seek

What is INDEX SCAN?

An Index Scan reads a large portion (or all) of the index.
SQL Server scans multiple rows/pages
Slower compared to seek (for large tables)
Happens when filtering is not selective

Example:

SELECT * FROM Employees
WHERE Name LIKE '%John%';

Leading wildcard prevents index usage → Index Scan

Key Differences

Feature	INDEX SEEK	INDEX SCAN
Data Access	Direct lookup	Sequential scan
Performance	Fast	Slower (large data)
Use Case	Exact/filtered queries	Broad/unfiltered queries
Efficiency	High	Low (for large tables)

When Does SQL Server Choose Each?

Index Seek:

WHERE Id = 10
WHERE Email = 'test@mail.com'
Proper indexing + selective condition

Index Scan:

WHERE Name LIKE '%abc%'
No index on column
Large result set

Important Note

Index Scan is not always bad
For small tables → scan can be faster
When most rows are needed → scan is logical

How to Improve (Convert Scan → Seek)

Add proper indexes
Avoid leading wildcards (%abc)
Use correct data types
Write optimized WHERE clauses

Example Optimization

Bad:

WHERE Name LIKE '%John%'

Better:

WHERE Name LIKE 'John%'

Final Thought

Index Seek = Fast, precise search
Index Scan = Broad, full scan

A good database design aims to maximize seeks and minimize unnecessary scans for better performance.

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What is difference between INDEX SEEK vs INDEX SCAN?

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1 Answers

What is INDEX SEEK?

What is INDEX SCAN?

Key Differences

When Does SQL Server Choose Each?

Index Seek:

Index Scan:

Important Note

How to Improve (Convert Scan → Seek)

Example Optimization

Final Thought