Creating same unique constraint with different names In MySQL 5.7


alter table mydb.roles add constraint uk1 unique (role_name);
alter table mydb.roles add constraint uk2 unique (role_name);


The 2nd alter command threw me a warning stating:


  Duplicate index 'uk2' defined on the table 'world_x.roles'. This is
  deprecated and will be disallowed in a future release.


When I tried the same in Postgres(10.x), it didn't warn me.

So, what would the SQL standard be in this scenario?
It can be result very confusing mixing names constraints and slow down your queries because they have the same name 

maybe this results helpful


  CREATE ONLY ONE CONSTRAINT INDEX AND INCLUDE THOSE NECESSARY COLUMNS


Example

ALTER TABLE users ADD CONSTRAINT findUser UNIQUE (nameUser,emailUser);


No double constraint and no warning message and you keep the SQL rules alive


  Remember SQL is an standard but not implemented at the same time for
  everyone with the same rules


As you can see at the following link, in fact these scenario is a bug

https://bugs.mysql.com/bug.php?id=37520

and finally recognized in: https://bugs.mysql.com/bug.php?id=8565

and finally fixed in MySQL Server 5.6.7