Showing all records that appear more than once

• j.clay 47557

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  October 10, 2018 at 2:24 am

  #380788

  Hi everyone
  I'm trying to write some SQL that will allow me to pull all records where the NUMBER column appears more than once. I need to see all the other columns too, whatever they contain e.g.

  NUMBER  COURSE  START  AWARD  GRADE    TYPE
  1                Biology      1988      BA          1st            Course
  1                Biology      1988      BA          1st            Course
  2                Maths        1975      MA          2:1           Course
  3                English      1987      BA          2:1            Course
  3                                  1987                                      Course

  So, in this example I would expect only NUMBERs 1 and 3 to be returned with the additional COURSE, START, AWARD and GRADE columns also showing. The idea behind this is to ensure that I can see all database records that have either duplicate information in them (e.g. NUMBER 1), or where part of the information is duplicated e.g. NUMBER 3.

  Any help would be much appreciated.

  Many thanks
  Jon

• John Mitchell-245523

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  October 10, 2018 at 2:42 am

  #2008768

  Jon

  Use COUNT(*) with a PARTITION BY clause to show the number of rows per NUMBER.  If you want to return only those rows with NUMBER greater than 1, you'll need to use a CTE or subquery, since you can't have COUNT(*) in your WHERE clause.

  John

• j.clay 47557

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  October 10, 2018 at 2:48 am

  #2008769

  OK, thanks John.

  I think that's above my SQL knowledge unfortunately. I'll do it the manual way 🙂

  Many thanks
  Jon

• Jeff Moden

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  October 10, 2018 at 7:46 am

  #2008821

  j.clay 47557 - Wednesday, October 10, 2018 2:48 AM

  OK, thanks John.

  I think that's above my SQL knowledge unfortunately. I'll do it the manual way 🙂

  Many thanks
  Jon

  Take the time to learn something new because you're going to need to do it again. 😉

  --Jeff Moden

  ---

  RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
  First step towards the paradigm shift of writing Set Based code:
  ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.

  Change is inevitable... Change for the better is not.
  

  ---

  Helpful Links:
  How to post code problems
  How to Post Performance Problems
  Create a Tally Function (fnTally)
  

• j.clay 47557

  SSC Eights!

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  October 10, 2018 at 7:49 am

  #2008822

  Very true and I will definitely learn. Deadlines are looming this week unfortunately 🙁

• ScottPletcher

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  October 10, 2018 at 11:13 am

  #2008900

  
SELECT tn.*
FROM (
    SELECT NUMBER
    FROM dbo.table_name
    GROUP BY NUMBER
    HAVING COUNT(*) > 1
) AS NUMBER_DUPS
INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
ORDER BY NUMBER, COURSE

  SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.

• drew.allen

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  Points: 76948

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  October 10, 2018 at 12:02 pm

  #2008915

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  J. Drew Allen
  Business Intelligence Analyst
  Philadelphia, PA

• ScottPletcher

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  October 10, 2018 at 12:56 pm

  #2008924

  drew.allen - Wednesday, October 10, 2018 12:02 PM

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  But then you don't list the first row of every NUMBER, right?

  SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.

• drew.allen

  SSC Guru

  Points: 76948

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  October 11, 2018 at 8:18 am

  #2009129

  ScottPletcher - Wednesday, October 10, 2018 12:56 PM

  drew.allen - Wednesday, October 10, 2018 12:02 PM

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  But then you don't list the first row of every NUMBER, right?

  Again, this is why we ask for expected results.  You would simply add a ROW_NUMBER to the CTE and select based on the row number = 1.  It will still probably perform faster than the self join.

  Drew

  J. Drew Allen
  Business Intelligence Analyst
  Philadelphia, PA

• drew.allen

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  Points: 76948

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  October 11, 2018 at 8:26 am

  #2009135

  ScottPletcher - Wednesday, October 10, 2018 12:56 PM

  drew.allen - Wednesday, October 10, 2018 12:02 PM

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  But then you don't list the first row of every NUMBER, right?

  Sorry, I looked back at the OP and realized that you were asking something else.

  Yes, it does include the first row.  A frame is only applied to a windowed function if there is an ORDER BY clause.  Since there was no ORDER BY clause specified in the windowed function, the COUNT is for the entire partition, so the count will be the same for all records in the partition (including the first).  This query will only exclude records where there is exactly one record in the partition.

  Drew

  J. Drew Allen
  Business Intelligence Analyst
  Philadelphia, PA

• Jonathan AC Roberts

  SSCoach

  Points: 18271

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  October 11, 2018 at 9:07 am

  #2009151

  drew.allen - Thursday, October 11, 2018 8:26 AM

  ScottPletcher - Wednesday, October 10, 2018 12:56 PM

  drew.allen - Wednesday, October 10, 2018 12:02 PM

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  But then you don't list the first row of every NUMBER, right?

  Sorry, I looked back at the OP and realized that you were asking something else.

  Yes, it does include the first row.  A frame is only applied to a windowed function if there is an ORDER BY clause.  Since there was no ORDER BY clause specified in the windowed function, the COUNT is for the entire partition, so the count will be the same for all records in the partition (including the first).  This query will only exclude records where there is exactly one record in the partition.

  Drew

  Nice way to do it. I've not seen this method before now.

• ScottPletcher

  SSC Guru

  Points: 100952

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  October 11, 2018 at 9:13 am

  #2009155

  Jonathan AC Roberts - Thursday, October 11, 2018 9:07 AM

  drew.allen - Thursday, October 11, 2018 8:26 AM

  ScottPletcher - Wednesday, October 10, 2018 12:56 PM

  drew.allen - Wednesday, October 10, 2018 12:02 PM

  ScottPletcher - Wednesday, October 10, 2018 11:13 AM

  
  SELECT tn.*
  FROM (
      SELECT NUMBER
      FROM dbo.table_name
      GROUP BY NUMBER
      HAVING COUNT(*) > 1
  ) AS NUMBER_DUPS
  INNER JOIN dbo.table_name tn ON tn.NUMBER = NUMBER_DUPS.NUMBER
  ORDER BY NUMBER, COURSE

  I suspect the following will perform better, but it's hard to test with no sample data.

  WITH Counts AS
(
 SELECT *, COUNT(*) OVER(PARTITION BY Number) AS cnt
 FROM dbo.table_name
)
SELECT *
FROM Counts
WHERE cnt > 1

  Drew

  But then you don't list the first row of every NUMBER, right?

  Sorry, I looked back at the OP and realized that you were asking something else.

  Yes, it does include the first row.  A frame is only applied to a windowed function if there is an ORDER BY clause.  Since there was no ORDER BY clause specified in the windowed function, the COUNT is for the entire partition, so the count will be the same for all records in the partition (including the first).  This query will only exclude records where there is exactly one record in the partition.

  Drew

  Nice way to do it. I've not seen this method before now.

  Interesting.  And, true, it will still list all rows. 

  But as to efficiency, doesn't SQL still have to do a separate query to get the COUNT?  Does it actually save any I/O?

  SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.