Solved

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

Posted on 2016-11-11
3
50 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:
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 28

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 77

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

Optimizing Cloud Backup for Low Bandwidth

With cloud storage prices going down a growing number of SMBs start to use it for backup storage. Unfortunately, business data volume rarely fits the average Internet speed. This article provides an overview of main Internet speed challenges and reveals backup best practices.

Question has a verified solution.

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

Slowly Changing Dimension Transformation component in data task flow is very useful for us to manage and control how data changes in SSIS.
Ever wondered why sometimes your SQL Server is slow or unresponsive with connections spiking up but by the time you go in, all is well? The following article will show you how to install and configure a SQL job that will send you email alerts includ…
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties
Viewers will learn how to use the UPDATE and DELETE statements to change or remove existing data from their tables. Make a table: Update a specific column given a specific row using the UPDATE statement: Remove a set of values using the DELETE s…

770 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