Solved

What's the difference between these two "qualifiers?"

Posted on 2016-11-11
3
66 Views
Last Modified: 2016-12-01
What's the difference between these two qualifiers:

datediff(d, max(t.created), getDate()) <= 45

and...

max(txn.created) > DATEADD(DAY, -45, GETDATE())

I'm thinking with the first one you have all of the rows where the t.created value falls within a range defined by the difference of today's date and whatever t.created values equals to 45 days or less.

The second clause is all of the rows that have a date that's greater than today's date minus 45 days.

Even when I attempt to explain that, I'm thinking they are fundamentally the same, but am I missing something?
0
Comment
Question by:brucegust
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
3 Comments
 
LVL 69

Accepted Solution

by:
Scott Pletcher earned 250 total points
ID: 41884260
datediff(d, max(t.created), getDate()) <= 45

= The number of calendar days (not necessarily 24-hour days) between t.created and the current date must be <= 45.


max(txn.created) > DATEADD(DAY, -45, GETDATE())

= The date and time in txn.created must be greater than the date and time 45 days before today.


The time factor is probably the most significant difference between them.
0
 
LVL 29

Assisted Solution

by:Pawan Kumar
Pawan Kumar earned 125 total points
ID: 41884421
Both are same if you consider the logic.

This <<datediff(d, max(t.created), getDate()) <= 45>> is really bad for performance as it will execute this expression for each row in the table and will lead to scanning the entire table even if you have index on the column.

This <<max(txn.created) > DATEADD(DAY, -45, GETDATE()) >> is good, since we are doing maths with the constant value and SQL will calculate the constant separately since it is not dependent on the any table.

Hope it helps !!
0
 
LVL 78

Assisted Solution

by:arnold
arnold earned 125 total points
ID: 41884665
the material difference is the logical comparison, one deals with integer comparison, the other performs datetime comparison.
The datetime comparison, can be simplified by assigning the date 45 days ago into a variable to avoid running dateadd for every row
Declare @date as datetime
Set @date=dateadd(d,-45,getdate())

Max(txt.created)>@date

Question is the cost of running datediff on every row of a result set less or more than datetime comparison, if not mistaken, the comparison on datetime also scans the entire result set datetime fields are not indexed........
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

JSON is being used more and more, besides XML, and you surely wanted to parse the data out into SQL instead of doing it in some Javascript. The below function in SQL Server can do the job for you, returning a quick table with the parsed data.
Load balancing is the method of dividing the total amount of work performed by one computer between two or more computers. Its aim is to get more work done in the same amount of time, ensuring that all the users get served faster.
This video shows how to set up a shell script to accept a positional parameter when called, pass that to a SQL script, accept the output from the statement back and then manipulate it in the Shell.
Via a live example, show how to shrink a transaction log file down to a reasonable size.

696 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question