Save and compare two plans

Two queries can return the same result through different strategies. Saving each plan as .sqlplan preserves the evidence and lets Compare Showplan align both structures.

Save evidence that can be opened again

A .sqlplan file contains Showplan XML. It can preserve operators, properties, statement text, and runtime counters. Review object names, predicates, literals, and other sensitive data before sharing it.

In SSMS, Save Execution Plan As is available from the plan canvas. Open one file and use Compare Showplan to choose the second. The top and bottom positions identify the files; they do not automatically mean “before” and “after.”

How to produce and open the comparison

1. Open a query window connected to the database that contains dbo.PedidoLaboratorio.
2. Enable Include Actual Execution Plan with Ctrl+M.
3. Run only the first query. Results should contain 136, while Execution plan contains that query’s plan.
4. Right-click an empty area of the plan, choose Save Execution Plan As, and save the file with a name that identifies the direct predicate.
5. Run only the second query and save its plan under another name.
6. Open either .sqlplan through File → Open → File. Right-click its canvas, choose Compare Showplan, and select the other file.

SSMS places one plan above the other. Verify the statement text before deciding which query occupies each position. Selecting equivalent operators exposes their top and bottom properties; press F4 if the Properties panel is not visible.

Two queries with the same result

The first query compares the date directly:

DECLARE @Desde date = '2025-01-01';

SELECT COUNT_BIG(*) AS Pedidos
FROM dbo.PedidoLaboratorio AS p
WHERE p.FechaPedido >= @Desde
OPTION (RECOMPILE);

The second transforms the column before comparing it:

DECLARE @Desde date = '2025-01-01';

SELECT COUNT_BIG(*) AS Pedidos
FROM dbo.PedidoLaboratorio AS p
WHERE DATEDIFF(DAY, @Desde, p.FechaPedido) >= 0
OPTION (RECOMPILE);

Both return 136 orders. Result equivalence is the starting point, not the performance conclusion.

Compare Showplan aligns the strategies

1. 1
   Top plan

   The query that transforms the column uses an Index Scan and reads the index before retaining 136 rows.

2. 2
   Bottom plan

   The direct predicate permits an Index Seek on the same index and returns the same 136 rows.

The comparison view locates branches and structural differences. It does not establish which alternative used fewer reads, CPU, or elapsed time.

Properties remain side by side

1. 1
   Top estimated cost

   The Index Scan plan shows an estimated subtree cost of 0.486179.

2. 2
   Bottom estimated cost

   The Index Seek plan shows 0.0035137. These are optimizer units, not milliseconds.

3. 3
   Plan identity

   Each side has a different QueryPlanHash, so these are not the same saved plan.

Also compare rows read and returned, predicates, warnings, memory, and execution counts. A cost percentage does not replace a baseline.

Comparing does not approve a change

The Scan–Seek difference produces a hypothesis: the direct predicate appears to require less work. Test it again with reads, CPU, and elapsed time, and confirm that the rewritten predicate preserves meaning for all relevant parameters.

What we can conclude

The saved files show two strategies for the same result. Compare Showplan aligns their structures and properties, but the decision still requires observed metrics and documented conditions.

A reasonable next check

The next entry uses Query Store to associate plans with time intervals and runtime statistics rather than relying on two manually selected files.

Related

• How Showplan XML is organized: understand what a .sqlplan file preserves.
• Build a repeatable baseline: define the comparison conditions.
• Actions available in the SSMS graphical plan: locate save and comparison actions.