updating column with value from another column in postgres table

Question

I have a postgres table which has 2 columns

username and email I have hundreds of rows in the table such as

username | email
username1 | [email protected]
username2 | [email protected]
username3 | [email protected]
username4 | [email protected]

The way this was setup all emails are the same, and now I need to make them unique. I am trying to update the email column to be like this

username | email
username1 | [email protected]
username2 | [email protected]
username3 | [email protected]
username4 | [email protected]

basically copy over the value from the username column and add it to the email column. I tried using the coalesce function but that will replace the value completely and not update it.

Please can you help me understand how to achieve this.

Thanks

Answer 1

An update with basic concatenation should work here:

UPDATE yourTable
SET email = username || '_' || email;