A few months ago I posted a little query about finding duplicate rows in a database table. I’m revisiting this because I helped out Doogie with a similar query last night but with some complications.
Let’s start with the original simple scenario of checking duplicates in a single column.
Some example data, a Users table:
+----+----------------+ | Id | Email | +----+----------------+ | 1 | joe@bloggs.com | | 2 | joe@bloggs.com | | 3 | joe@bloggs.com | | 4 | jane@doe.com | | 5 | jane@doe.com | | 6 | john@doe.com | +----+----------------+
You can see that joe@bloggs.com and jane@doe.com have been duplicated. This could have been prevented by putting a unique index on the Email column.
So to find what emails have duplicates in our table:
Continue reading Finding duplicated data across one or more columns in a database table
