SQL

 Search and delete duplicate records

SELECT email
FROM users
GROUP BY email
HAVING ( COUNT(email) > 1 )

This works also for multiple columns

SELECT col1, col2,col3,count(col3)--put the last column of duplicate combination in Count()
FROM table1
GROUP BY col1,col2,col3
HAVING COUNT(col3) >1

To delete one of the records if you have a primary key

CREATE TABLE tmptable
SELECT min(primary_key) as primary_key, col1, col2,col3,count(col3)--put the last column of duplicate combination in Count()
FROM table1
GROUP BY col1,col2,col3
HAVING COUNT(col3) >1
-- Now you have all the first duplicate record keys in tmptable
DELETE FROM table1 where primary_key in (SELECT primary_key FROM tmptable)
DROP TABLE tmptable

Repeat until nothing is selected