Alter table supports adding or removing columns from primary key

[killme2008]

What type of enhancement is this?

API improvement, User experience

What does the enhancement do?

Alter table statement must support adding or removing columns from primary key, maybe like:

ALTER TABLE table_name   
MODIFY PRIMARY KEY REMOVE (column1, column2, ...);  

ALTER TABLE table_name   
MODIFY PRIMARY KEY add (column1, column2, ...);  

Implementation challenges

No response

[evenyag]

It's not easy to remove an existing column from or add an existing column to the primary key because the order of rows will change.

We also assume all rows are sorted in the same order in the storage engine. Maybe we can do this by copying an existing table and then rename them.