@Override
  public List<SQLCheckConstraint> addCheckConstraints(List<SQLCheckConstraint> nns)
      throws InvalidObjectException, MetaException {
    return addCheckConstraints(nns, true);
  }
Called right before an action that would drop a storage descriptor.
This function makes the SD's reference to a CD null, and then deletes the CD
if it no longer is referenced in the table.
@param msd the storage descriptor to drop
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java