Формат
<unique constraint definition> ::=
<unique specification> (<unique column list>)
<unique specification> ::=
UNIQUE | PRIMARY KEY
<unique column list> ::=
<column name> [{,<column name>}...]
<unique constraint definition> ::=
<unique specification> (<unique column list>)
<unique specification> ::=
UNIQUE | PRIMARY KEY
<unique column list> ::=
<column name> [{,<column name>}...]