GET_PARAMS_FROM_QUERY_STRING for BigQuery

GET_PARAMS_FROM_QUERY_STRING.SQL

CREATE TEMPORARY FUNCTION GET_PARAMS_FROM_QUERY_STRING(query_str STRING, key_name STRING)
RETURNS STRING
LANGUAGE js AS """
if (query_str == null) { return null; }
var start = 0;
while (0 <= start && start < query_str.length) {
  var end = query_str.indexOf('&', start + 1);
  if (end < 0) { end = query_str.length }
  
  var p = query_str.indexOf('=', start);
  if (0 <= p && p < end) {
    var k = query_str.substr(start, p - start);
    if (k == key_name) {
      var v = query_str.substr(p+1, end - p - 1);
      return decodeURIComponent(v);
    }
  }
  start = end + 1;
}
return null;
""";