private boolean isUserCreationTimeMigrated() throws SQLException {
    final int columnType = dbAccessor.getColumnType(USERS_TABLE, USERS_CREATE_TIME_COLUMN);
    LOG.info(USERS_TABLE + "." + USERS_CREATE_TIME_COLUMN + "'s type = " + columnType);
    return columnType != Types.DATE && columnType != Types.TIMESTAMP;
  }
In order to save the epoch equivalent of users.create_time we need to convert data in this column as follows:
<ol>
<li>creating a temporary column where we store the numeric representation of
the timestamp
<li>populating data in the temporary column
<li>removing original column column
<li>renaming the temporary column to the original column
</ol>

@throws SQLException
          if an error occurs while executing SQL statements
ambari-server/src/main/java/org/apache/ambari/server/upgrade/UpgradeCatalog270.java