I have a table in MySQL of contact information ;
first name, last name, address, etc.
I would like to run a query on this table that will return only rows with first and last name combinations which appear in the table more than once.
I do not want to group the "duplicates" (which may only be duplicates of the first and last name, but not other information like address or birthdate) -
I want to return all the "duplicate" rows so I can look over the results and determine if they are dupes or not. This seemed like it would be a simple thing to do, but it has not been.
开发者_运维技巧Every solution I can find either groups the dupes and gives me a count only (which is not useful for what I need to do with the results) or doesn't work at all.
Is this kind of logic even possible in a query ? Should I try and do this in Python or something?
You should be able doing this with the GROUP BY
approach in a sub-query.
SELECT t.first_name, t.last_name, t.address
FROM your_table t
JOIN ( SELECT first_name, last_name
FROM your_table
GROUP BY first_name, last_name
HAVING COUNT(*) > 1
) t2
ON ( t.first_name = t2.first_name, t.last_name = t2.last_name )
The sub-query returns all names (first_name
and last_name
) that exist more than once, and the JOIN
returns all records that match these names.
You could do it with a GROUP BY / HAVING and A SUB SELECT. Something like
SELECT t.*
FROM Table t INNER JOIN
(
SELECT FirstName, LastName
FROM Table
GROUP BY FirstName, LastName
HAVING COUNT(*) > 1
) Dups ON t.FirstName = Dups.FirstName
AND t.LastName = Dups.LastName
select * from people
join (select firstName, lastName
from people
group by firstName, lastName
having count(*) > 1
) dupe
using (firstName, lastName)
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