Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

Newbie Question: How to implement example code?

Posted on 2008-10-16
7
Medium Priority
?
174 Views
Last Modified: 2010-04-21
Hi All,
I'm brand new to SQL but can usually pick up programming pretty easy so this is frustrating. When I see the example code for this solution, I'm not sure how to interpret it. Excuse my ignorance, please!!

When this code says to select "r", is that a dummy table name or is the user meant to insert the name of the table with the data in it? And is create_date something you leave in there, or do you define it elsewhere, or insert your own date? Is rev_id the id you want to group by?

Just simple, quick descriptions of what these terms are referring to would help me so much and would be greatly appreciated.
select r.* from review as r
inner join 
(
select rev_id,max(create_date) as max_dat
from review
group by rev_id
) as rev_max  on r.rev_id = rev_max.rev_id and r.create_date = rev_max.create_date

Open in new window

0
Comment
Question by:chaimberbell
[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
  • 4
  • 3
7 Comments
 
LVL 7

Expert Comment

by:natloz
ID: 22731660
select r.* from review as r

This statemet "from review as r" has aliased "r" as the new table name which can than be used in the query....
0
 
LVL 7

Accepted Solution

by:
natloz earned 500 total points
ID: 22731689
"r" now represents the table "review"

you could go...

select a.value, b.value
from tblApple a
inner join tblBanana b on pkFruitID = fkFruitID
where a.value = 'green' and b.value = 'yellow'

a = tblApple
b = tblBanana
0
 

Author Comment

by:chaimberbell
ID: 22731779
Ah, thanks. That part makes more sense now.

What about the create_date part?
0
Simplifying Server Workload Migrations

This use case outlines the migration challenges that organizations face and how the Acronis AnyData Engine supports physical-to-physical (P2P), physical-to-virtual (P2V), virtual to physical (V2P), and cross-virtual (V2V) migration scenarios to address these challenges.

 
LVL 7

Expert Comment

by:natloz
ID: 22731825
create_date looks like it is simply a field in "review" that is being passed into the MAX function to gets the maximum value found.
0
 
LVL 7

Expert Comment

by:natloz
ID: 22731864
Depending on what you are trying to combine will determine what you want to group by.
If there is only one create_date per review and you are looking for the max of create_date, I would probably group by create_date and remove rev_id from the query, since any field in a query that has an aggregate function (such as MAX) has to be in the group by statement.
0
 

Author Closing Comment

by:chaimberbell
ID: 31506766
Thanks!
0
 

Author Comment

by:chaimberbell
ID: 22731911
I missed that those were the names of the fields. Thanks for clarifying! I'm gonna give it a try now :-).
0

Featured Post

Survive A High-Traffic Event with Percona

Your application or website rely on your database to deliver information about products and services to your customers. You can’t afford to have your database lose performance, lose availability or become unresponsive – even for just a few minutes.

Question has a verified solution.

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

What if you have to shut down the entire Citrix infrastructure for hardware maintenance, software upgrades or "the unknown"? I developed this plan for "the unknown" and hope that it helps you as well. This article explains how to properly shut down …
This article shows how to get a list of available printers for display in a drop-down list, and then to use the selected printer to print an Access report or a Word document filled with Access data, using different syntax as needed for working with …
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
In this video, Percona Solutions Engineer Barrett Chambers discusses some of the basic syntax differences between MySQL and MongoDB. To learn more check out our webinar on MongoDB administration for MySQL DBA: https://www.percona.com/resources/we…

715 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