'Return information about the primary key constraint on
table_name`.
Given a :class:`.Connection`, a string
`table_name`, and an optional string `schema`, return primary
key information as a dictionary with these keys:
constrained_columns
a list of column names that make up the primary key
name
optional name of the primary key constraint.'

def get_pk_constraint(self, connection, table_name, schema=None, **kw):

    raise NotImplementedError()
