SQL if not null update

Question

I have this query

UPDATE users SET username = Param1,email = Param2,PASSWORD = Param3 WHERE id = Param4;

this is updating my user row, but

Answer 1

Like this

UPDATE users 
SET 
  username = Param1,
  email = COALESCE(Param2, email),
  password = COALESCE(Param3, password)
WHERE id = Param4;

COALESCE works from left to right taking the first non null argument. If you provide null as Param2, it will update email to email (no change). If you provide a value to Param2, coalesce will return that non null value so email is updated to whatever param2 is

Ps: understood your request to be "I will provide either a null or a value in the parameter. If I provide a null I don't want to update the db table. If I provide a value I do want to update the DB table"

This seemed more logical to me than how your question reads which is "if my table value is null for email then I forever want it to remain null and never want any of the values I supply in the parameters to be written to the table"