public PrimaryKeyInfo getPrimaryKeyInfo() {
    if (!isTableConstraintsFetched) {
      getTableConstraintsInfo();
    }
    return tableConstraintsInfo.getPrimaryKeyInfo();
  }
Constraints related methods
 Note that set apis are used by DESCRIBE only, although get apis return RELY or ENABLE
 constraints DESCRIBE could set all type of constraints
ql/src/java/org/apache/hadoop/hive/ql/metadata/Table.java