How to delete records with duplicate fields, such as dupplicate emails?

To delete records where only a field is duplicated, we can use a similar technique to the general duplicate removal technique:

CREATE TABLE temp AS SELECT DISTINCT ON (email) * FROM table_to_deduplicate;
DROP TABLE table_to_deduplicate;
ALTER TABLE temp RENAME TO table_to_deduplicate;

Be mindful of the fact that this process will not preserve the constraints on the original table. So if you have indexes, NOT NULL attributes, primary keys, foreign keys, you’ll have to recreate them.