Unnecessary sort with TOP PERCENT?

### Setup

-- Create a heap table of numbers from 1 to 100
SELECT TOP (100)
    i = IDENTITY(int, 1, 1)
INTO #T
FROM master.dbo.spt_values;

-- Add a clustered primary key
ALTER TABLE #T
    ADD PRIMARY KEY CLUSTERED (i);

### Test query Display 9% of the rows in primary key order:

SELECT TOP (9e) PERCENT 
    i 
FROM #T 
ORDER BY 
    i ASC;

DROP TABLE #T;

dbfiddle demo ### Results ### Execution plan --- ## Question Why does SQL Server sort the column when the clustered index provides exactly that order? --- ### More rows If I increase the number of rows in the table, I get an Eager Spool instead of a Sort and the index is scanned in order:

-- Create a heap table of numbers from 1 to 1,000
SELECT TOP (1000)
    i = IDENTITY(int, 1, 1)
INTO #T
FROM master.dbo.spt_values;

-- Add a clustered primary key
ALTER TABLE #T
    ADD PRIMARY KEY CLUSTERED (i);

-- 0.9% now
SELECT TOP (9e-1) PERCENT 
    i 
FROM #T 
ORDER BY 
    i ASC;

DROP TABLE #T;