Building on yesterday’s blog post about how a query is processed this post will show you how a query processes the Not Equal To operator.
As I explained in my last post, when a query is run it will process each row within a view or a table. Using the following table as our example, let’s look at the how the Not Equal To operator is processed in a query. This table is comprised of 4 PCs and their add/remove program (ARP) details.
|
PC Name |
PC1 |
PC2 |
PC3 |
PC4 |
|
1 |
Adobe Reader XI |
Microsoft Project 2010 |
Visio 12 |
Adobe Reader X |
|
2 |
Visio 12 |
CorelDraw |
ITunes |
Microsoft Project 2010 |
|
3 |
ITunes |
Office 2010 |
WordStar |
DataStar |
|
4 |
Microsoft Office 2013 |
|
|
Lotus123 |
|
5 |
|
|
|
Kix 2010 |
Don’t forget, we’re trying to find all of the PCs that do not have Microsoft Project 2010 installed.
1. Starting at PC1 the query will review each row to look for Microsoft Project 2010.
a. Row 1 is added to the result set since it is not equal to Microsoft Project 2010.
b. Row 2 is added to the result set since it is not equal to Microsoft Project 2010.
c. Row 3 is added to the result set since it is not equal to Microsoft Project 2010.
d. Row 4 is added to the result set since it is not equal to Microsoft Project 2010.
2. The process is repeated for PC2.
a. Row 2 is added to the result set since it is not equal to Microsoft Project 2010.
b. Row 3 is added to the result set since it is not equal to Microsoft Project 2010.
3. The process is repeated with PC3.
a. Row 1 is added to the result set since it is not equal to Microsoft Project 2010.
b. Row 2 is added to the result set since it is not equal to Microsoft Project 2010.
c. Row 3 is added to the result set since it is not equal to Microsoft Project 2010.
4. The process is repeated with PC4.
a. Row 1 is added to the result set since it is not equal to Microsoft Project 2010.
b. Row 3 is added to the result set since it is not equal to Microsoft Project 2010.
c. Row 4 is added to the result set since it is not equal to Microsoft Project 2010.
d. Row 5 is added to the result set since it is not equal to Microsoft Project 2010.
5. Finally the query will return PC1, PC2, PC3 and PC4 to the result set as each of them has a row that is Not Equal To Microsoft Project 2010.
As you can see above the Not Equal To operator will not give us the results that we are looking for, so in next week’s blog post I will show you the importance of using a subselect query. If you have any questions about this post, please feel free to contact me @GarthMJ, or leave a note in the comment section below.
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