将角色"列添加到表中

 alter table School
    add (Role   varchar(10));

向角色"列添加约束.

alter table School
  add constraint check_role
  check (Role IN ('Teaching Assistant', 'Lecturer', 'Professor'));

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ALTER TABLE School ADD COLUMN Role VARCHAR(50) 
CONSTRAINT check_role CHECK 
  (Role IN ('Teaching Assistant', 'Lecturer', 'Professor'));