/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* 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
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "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.
*/
package org.apache.hadoop.hive.ql.udf.generic;
import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.UDFType;
@Description(
name = "lag",
value = "LAG (scalar_expression [,offset] [,default]) OVER ([query_partition_clause] order_by_clause); "
+ "The LAG function is used to access data from a previous row.",
extended = "Example:\n "
+ "select p1.p_mfgr, p1.p_name, p1.p_size,\n"
+ " p1.p_size - lag(p1.p_size,1,p1.p_size) over( distribute by p1.p_mfgr sort by p1.p_name) as deltaSz\n"
+ " from part p1 join part p2 on p1.p_partkey = p2.p_partkey")
@UDFType(impliesOrder = true)
public class GenericUDFLag extends GenericUDFLeadLag {
@Override
protected String _getFnName() {
return "lag";
}
@Override
protected int getIndex(int amt) {
return pItr.getIndex() - 1 - amt;
}
@Override
protected Object getRow(int amt) throws HiveException {
return pItr.lag(amt + 1);
}
}