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   regarding copyright ownership.  The ASF licenses this file
   to you under the Apache License, Version 2.0 (the
   "License"); you may not use this file except in compliance
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   "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   KIND, either express or implied.  See the License for the
   specific language governing permissions and limitations
   under the License. :)

(: XQuery Self Join Query :)
(: Self join with all stations finding the difference in min and max       :)
(: temperature and get the average.                                        :)
    let $sensor_collection_min := "ghcnd_half_1|ghcnd_half_2"
    for $r_min in collection($sensor_collection_min)/dataCollection/data
    
    let $sensor_collection_max := "ghcnd_half_1|ghcnd_half_2"
    for $r_max in collection($sensor_collection_max)/dataCollection/data
    
    where $r_min/station eq $r_max/station
        and $r_min/date eq $r_max/date
        and $r_min/dataType eq "TMIN"
        and $r_max/dataType eq "TMAX"
    return $r_max/value - $r_min/value