Why should you care?

Plans turn “it’s slow” into “clustered index scan of 2M rows” — actionable.

See it live — copy this example

Run in SQL Server Management Studio (SSMS) or Azure Data Studio.

USE DataVerse;
SET STATISTICS XML ON; -- or click Include Actual Execution Plan in SSMS
SELECT o.OrderId, c.FullName
FROM dbo.Orders o
JOIN dbo.Customers c ON c.CustomerId = o.CustomerId
WHERE o.City = N'Mumbai';
SET STATISTICS XML OFF;

What happened?

• STATISTICS XML returns the plan as XML (SSMS renders it graphically).
• Look for thick arrows, scans, and big differences between estimated and actual rows.

Practice next

1. Enable Include Actual Execution Plan.
2. Run the join query.
3. Hover operators and read row counts.
4. Compare INNER HASH JOIN hint vs default (lab curiosity).
5. Look for Implicit Conversion warnings.

Remember

Plans reveal operators and costs. Prefer actual plans for tuning. Fix the expensive operator first.

Slow join found in plan

DataVerse support query scanned Orders.

Outcome: Index on City + CustomerId fixed the seek.