how to select rows based on distinct values of A COLUMN only
I need to query a table in order to return rows, but I am not able to query the table correctly. Here is my table view:
Id MailId EmailAddress Name 1 1 email@example.com Mr. A 2 1 firstname.lastname@example.org Mr. B 3 1 email@example.com Mr. C 4 1 firstname.lastname@example.org Mr. D 5 1 email@example.com Mr. A 6 2 firstname.lastname@example.org Mr. E 7 2 email@example.com Mr. A 8 3 firstname.lastname@example.org Mr. F 9 4 email@example.com Mr. D 10 5 firstname.lastname@example.org Mr. F 11 6 email@example.com Mr. D
The result set should return:
Id MailId EmailAddress Name 1 1 firstname.lastname@example.org Mr. A 2 1 email@example.com Mr. B 3 1 firstname.lastname@example.org Mr. C 4 1 email@example.com Mr. D 6 2 firstname.lastname@example.org Mr. E 8 3 email@example.com Mr. F
In other words: first, I want to select distinct e-mail addresses, and then return rows containing distinct e-mail addresses.
Note: Just using the “Distinct” keyword will not work here, as it will select distinct rows. My requirement is to select distinct email addresses, and then to select rows containing those addresses.
Edit: I cannot use the “Group By” keyword either, because for this I will also have to Group By with Id (which is the PK) and doing this will return two rows with the same EmailAddress values but with different Ids.
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Looking at your output maybe the following query can work, give it a try:
SELECT * FROM tablename WHERE id IN (SELECT MIN(id) FROM tablename GROUP BY EmailAddress)
This will select only one row for each distinct email address, the row with the minimum
id which is what your result seems to portray
Try this – you need a CTE (Common Table Expression) that partitions (groups) your data by distinct e-mail address, and sorts each group by ID – smallest first. Then you just select the first entry for each group – that should give you what you’re looking for:
;WITH DistinctMails AS ( SELECT ID, MailID, EMailAddress, NAME, ROW_NUMBER() OVER(PARTITION BY EMailAddress ORDER BY ID) AS 'RowNum' FROM dbo.YourMailTable ) SELECT * FROM DistinctMails WHERE RowNum = 1
This works on SQL Server 2005 and newer (you didn’t mention what version you’re using…)
if you dont wanna use DISTINCT use GROUP BY
SELECT * FROM myTABLE GROUP BY EmailAddress
use this(assume that your table name is emails):
select * from emails as a inner join (select EmailAddress, min(Id) as id from emails group by EmailAddress ) as b on a.EmailAddress = b.EmailAddress and a.Id = b.id
hope this help..
I am not sure about your DBMS. So, I created a temporary table in Redshift and from my experience, I think this query should return what you are looking for:
select min(Id), distinct MailId, EmailAddress, Name from yourTableName group by MailId, EmailAddress, Name
I see that I am using a
GROUP BY clause but you still won’t have two rows against any particular