Solved

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

Posted on 2016-11-11
3
35 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
3 Comments
 
LVL 69

Accepted Solution

by:
ScottPletcher 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 18

Assisted Solution

by:Pawan Kumar Khowal
Pawan Kumar Khowal 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 76

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

Highfive + Dolby Voice = No More Audio Complaints!

Poor audio quality is one of the top reasons people don’t use video conferencing. Get the crispest, clearest audio powered by Dolby Voice in every meeting. Highfive and Dolby Voice deliver the best video conferencing and audio experience for every meeting and every room.

Join & Write a Comment

When you hear the word proxy, you may become apprehensive. This article will help you to understand Proxy and when it is useful. Let's talk Proxy for SQL Server. (Not in terms of Internet access.) Typically, you'll run into this type of problem w…
This article explains how to reset the password of the sa account on a Microsoft SQL Server.  The steps in this article work in SQL 2005, 2008, 2008 R2, 2012, 2014 and 2016.
This videos aims to give the viewer a basic demonstration of how a user can query current session information by using the SYS_CONTEXT function
Via a live example, show how to setup several different housekeeping processes for a SQL Server.

746 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

Need Help in Real-Time?

Connect with top rated Experts

11 Experts available now in Live!

Get 1:1 Help Now