How to remove a row from the database on update to avoid conflict?

Question

PostgreSQL

Actually I have a table which consists of fields

• microservice_id
  
• transport_id
  
• username
  
• password
  
• is_default
  

and unique key (microservice_id, transport_id)
I am trying to make a request

UPDATE microservices_transports
SET
  transport_id = :next,
  username     = :username,
  password     = :password,
  is_default   = COUNT((SELECT *
                        FROM
                          (DELETE FROM microservices_transports AS mt WHERE mt.transport_id = :next AND mt.microservice_id = microservice_id RETURNING *)
                        WHERE is_default = TRUE
                       )) > 0
WHERE
  transport_id = :prev

But he swears at the syntax about DELETE. I don't know how else to do this kind of action. Are there any easier or better ways?

Answer 1

After FROM there should be a table name, and you have a deletion there that returns *

Answer 2

What to make select from delete it is necessary that this delete returned something. You don't have it. You need returning in delete