• Power Query Is No Longer DAX’s Little Brother

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    I’ve talked before about the difference between the Power Query Formula language, or M, and the DAX language.

    I would describe Power Query as the intern you pay minimum wage or the sous chef, and DAX as the $35 per hour analyst or the head chef. This wasn’t to be mean but instead was just because Power Query was all about automating repetitive data manipulations. It handled the less exciting, less complicated work.

    Last week, however, I presented on Power Query, and I had to update the slide about where it’s available. I used to say that wherever DAX is, Power Query was not very far behind. Doing all of the grunt work so that DAX could shine. But this time I had to update my slides because Power Query is starting to take center stage.

    Now instead of just being available in Excel, Power BI and SSAS, Power Query is available in Microsoft Flow, SSIS and ADF! At the time this post was published, these are all in preview. But it’s really exciting to see Power Query no longer trailing behind DAX, ready to take center stage.

  • T-SQL Tuesday #114 – An Unsolved SQL Puzzle

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    This week’s T-SQL Tuesday invitation is all about puzzles. I’ve got an accidental puzzle that I’ve never quite solved, from one of my demos. I’m sure the answer will be a “Well duh!” moment.

    I give presentations on SQL Server execution plans. As part of that, I like to show that if you pull a single row from a heap, it has to read everything. As part of that demo, I try to push everything out of memory by disabling readahead reads, taking a checkpoint, and dropping clean buffers. But for some reason… it never quite works!

    IF NOT EXISTS ( SELECT  *
FROM    sys.schemas
WHERE   name = N'Demo' )
EXEC('CREATE SCHEMA [Demo] AUTHORIZATION [dbo]');
GO

IF OBJECT_ID('Adventureworks2014.Demo.Person', 'U') IS NOT NULL
BEGIN
DROP TABLE AdventureWorks2014.Demo.Person;
END

SET STATISTICS IO ON

SELECT *
INTO [AdventureWorks2014].[Demo].[Person]
FROM [AdventureWorks2014].[Person].[Person]

DBCC TRACEON (652,-1);

CHECKPOINT
DBCC DROPCLEANBUFFERS

SELECT * FROM [AdventureWorks2014].[Demo].[Person]
WHERE BusinessEntityID = 25

    You can see here that it shows 3,808 logical reads, but 5 physical reads.

    Screen shot of statistics IO showing the number of reads.

    I’m sure there is some simple way to force it to do all of the physical reads, but I have yet to figure it out. Or it may be that I’m misunderstanding something and physical reads are the only pages used. But when I look at the execution plan, it says it read all of the rows.

    I’d love to get an answer to this puzzle. I’m sure it’s something simple.

    Update: Andy G. asked if maybe the issue is I’m not using all the rows. Here I tried a heap of a single row, and I get 1 logical read and 0 physical reads.

    Table 'Person'. Scan count 1, logical reads 1, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

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