How Much Can One Row Change A Plan, Part 3

All The Rage

We’ve asked how much one column and even one row can change a plan before.

The doctor says I’m not allowed to read blog comments anymore on account of my blood pressure, but the AI I wrote in PowerShell assures me they were well-received.

So here we go again, ONCE MORE INTO THE FRAY!

Or is it ONCE MORE UNTO THE BREACH?

Eh, books.

Let’s SQL

Here’s contestant number one:

SELECT      TOP 3   c.Id
FROM        dbo.Comments AS c
WHERE       NOT EXISTS (   SELECT   *
                           FROM     dbo.Votes AS v
                           WHERE    c.PostId = v.PostId )
ORDER BY    c.CreationDate DESC;

And the results from stats time and IO:

Table 'Comments'. Scan count 7, logical reads 159138, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Votes'. Scan count 7, logical reads 287662, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Workfile'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 88672 ms,  elapsed time = 16255 ms.

Here’s contestant number two:

SELECT      TOP 2   c.Id
FROM        dbo.Comments AS c
WHERE       NOT EXISTS (   SELECT   *
                           FROM     dbo.Votes AS v
                           WHERE    c.PostId = v.PostId )
ORDER BY    c.CreationDate DESC;

And the results from stats time and IO:

Table 'Votes'. Scan count 1, logical reads 1375434, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Comments'. Scan count 1, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

 SQL Server Execution Times:
   CPU time = 21156 ms,  elapsed time = 21150 ms.

Tally up

Trade offs

So uh

I’ll follow up when I finish my math degree.

Or later this week.

Thanks for reading!