Drastically shorten your training time with WalkMe's advanced online training solution that Guides your trainees to action.
Course Of The Month
8 days, 11 hours left to enrollBecome a Premium Member and unlock a new, free course in leading technologies each month.
Solved
MS SQL - Remove Duplicate Values in a Column & Display All Columns (Not DISTINCT)
Posted on 2014-11-26
Dear Experts,
In my query result I need to show results from a SQL alarms history table for 5 columns where Col1 = Date&Time, Col2 = Label, Col3 = Priority, Col4 = Status, Col5 = Cycle. I am using the following syntax which shows everything.
SELECT TOP 50 App_DateTime, Label, Priority, Enum_Status, Cycle FROM History
However because an alarm is recorded every time it cycles (ON/OFF) it is recorded as a new entry into the database with a unique Date&Time. This produces duplicate column values for Label, Priority and Status. I want to display only the maximum Cycle count for each alarm entry and not all the Cycle values below that for the same alarm. Therefore I want to eliminate duplicate entries in the Label column.
The problem I have in using 'GROUP BY Label' is that when I apply aggregates to all the other SELECT fields to allow the GROUP BY to function to work then I only get a single row result. I am expecting to see a list of different alarms together with their date, time, label, priority and status and maximum cycle value.
I am new to SQL so may well be approaching this the wrong way. I have searched around and tried using SELECT DISTINCT but that will eliminate a row only if all its fields are the same. Clearly this wont work for me since I am trying to eliminate duplicate values from a column and not duplicate rows.
Thanks, Gary
In my query result I need to show results from a SQL alarms history table for 5 columns where Col1 = Date&Time, Col2 = Label, Col3 = Priority, Col4 = Status, Col5 = Cycle. I am using the following syntax which shows everything.
SELECT TOP 50 App_DateTime, Label, Priority, Enum_Status, Cycle FROM History
However because an alarm is recorded every time it cycles (ON/OFF) it is recorded as a new entry into the database with a unique Date&Time. This produces duplicate column values for Label, Priority and Status. I want to display only the maximum Cycle count for each alarm entry and not all the Cycle values below that for the same alarm. Therefore I want to eliminate duplicate entries in the Label column.
The problem I have in using 'GROUP BY Label' is that when I apply aggregates to all the other SELECT fields to allow the GROUP BY to function to work then I only get a single row result. I am expecting to see a list of different alarms together with their date, time, label, priority and status and maximum cycle value.
I am new to SQL so may well be approaching this the wrong way. I have searched around and tried using SELECT DISTINCT but that will eliminate a row only if all its fields are the same. Clearly this wont work for me since I am trying to eliminate duplicate values from a column and not duplicate rows.
Thanks, Gary
[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
2
3 Comments
Active 2 days ago
SELECT TOP (50) App_DateTime, Label, Priority, Enum_Status, Cycle
FROM (
SELECT App_DateTime, Label, Priority, Enum_Status, Cycle,
ROW_NUMBER() OVER(PARTITION BY Label ORDER BY Cycle DESC) AS row_num
FROM History
) AS subquery1
WHERE
row_num = 1
--ORDER BY <whatever>
FROM (
SELECT App_DateTime, Label, Priority, Enum_Status, Cycle,
ROW_NUMBER() OVER(PARTITION BY Label ORDER BY Cycle DESC) AS row_num
FROM History
) AS subquery1
WHERE
row_num = 1
--ORDER BY <whatever>
Hi Scott, thanks for your answer. You wouldn't believe how long I have been trying to put this together. A brief explanation of how the query works would be very much appreciated for us SQL novices. G
Active 2 days ago
I actually do believe it :-). It was a real pain to do certain things like this before ROW_NUMBER() came along.
Basically ROW_NUMBER() provides an inline ordering that resets to 1 on each PARTITION break.
For example, say you had a list of states and cities. You could PARTITION BY state ORDER BY city, and you'd get a result like:
1 CA Sacramento
2 CA San Diego
3 CA San Francisco
1 TN Memphis --note that the state change causes the number to reset
2 TN Nashville --
1 WY ...
Now, let's go back to:
PARTITION BY Label ORDER BY Cycle DESC
We can see that ROW_NUMBER/row_num 1 will always be the highest cycle number for each label, which is what we want to list, so we restrict the output to:
row_num = 1
This is wonderfully useful/flexible. For example, to get the top 3, you could use:
row_num BETWEEN 1 AND 3
How sweet is that!
Basically ROW_NUMBER() provides an inline ordering that resets to 1 on each PARTITION break.
For example, say you had a list of states and cities. You could PARTITION BY state ORDER BY city, and you'd get a result like:
1 CA Sacramento
2 CA San Diego
3 CA San Francisco
1 TN Memphis --note that the state change causes the number to reset
2 TN Nashville --
1 WY ...
Now, let's go back to:
PARTITION BY Label ORDER BY Cycle DESC
We can see that ROW_NUMBER/row_num 1 will always be the highest cycle number for each label, which is what we want to list, so we restrict the output to:
row_num = 1
This is wonderfully useful/flexible. For example, to get the top 3, you could use:
row_num BETWEEN 1 AND 3
How sweet is that!
Featured Post
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.
This article shows gives you an overview on SQL Server 2016 row level security. You will also get to know the usages of row-level-security and how it works
Using examples as well as descriptions, and references to Books Online, show the documentation available for date manipulation functions and by using a select few of these functions, show how date based data can be manipulated with these functions.
Via a live example, show how to backup a database, simulate a failure backup the tail of the database transaction log and perform the restore.
Suggested Courses
Earn Certification
HTML5 Specialist - Certification
Free withPremium
Course of the Month8 days, 11 hours left to enroll
617 members asked questions and received personalized solutions in the past 7 days.
Join the community of 500,000 technology professionals and ask your questions.