@Override
  public String getDisplayString(String[] children) {
    assert (children.length == 2 || children.length == 3);
    return getStandardDisplayString("locate", children);
  }
Generic UDF for string function <code>LOCATE(substr, str)</code>,
<code>LOCATE(substr, str, start)</code>. This mimcs the function from MySQL
http://dev.mysql.com/doc/refman/5.1/en/string-functions.html#function_locate

<pre>
usage:
LOCATE(substr, str)
LOCATE(substr, str, start)
</pre>
<p>
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFLocate.java