Hive 访问上一行值

Question

I have the same issue mentioned here

However, the problem is on Hive database. When I try the solution on my table that looks like

Id   Date             Column1    Column2
1    01/01/2011       5          5 => Same as Column1
2    02/01/2011       2          18 => (1 + (value of Column2 from the previous row)) * (1 + (Value of Column1 from the current row)) i.e. (1+5)*(1+2)
3    03/01/2011       3          76 => (1+18)*(1+3) = 19*4

I get the error

FAILED: SemanticException Recursive cte cteCalculation detected (cycle: ctecalculation -> cteCalculation).

What is the workaround possible in this case

Answer 1

You will have to write a UDF for this.
Below you can see a very (!!) simplified UDF for what you need.
The idea is to store the value from the previous execution in a variable inside the UDF and each time return (stored_value+1)*(current_value+1) and then store it for the next line.
You need to take care of the first value to get, so there is a special case for that.
Also, you have to pass the data ordered to the function as it simply goes line by line and performs what you need without considering any order.

You have to add your jar and create a function, lets call it cum_mul .

The SQL will be :

select id,date,column1,cum_mul(column1) as column2
from
(select id,date,column1 from myTable order by id) a  

The code for the UDF :

import org.apache.hadoop.hive.ql.exec.UDF;

public class cum_mul extends UDF  {

    private int prevValue;
    private boolean first=true;

    public int evaluate(int value) {
        if (first) {
            this.prevValue = value;
            first = false;
            return value; 
        }
        else {
            this.prevValue = (this.prevValue+1)*(value+1);
            return this.prevValue;      
        }
      }
}

Answer 2

Hive common table expression (CTE) works as a query level temp-table (a syntax sugar) that is accessible within the whole SQL.

Recursive query is not supported because it introduces multiple stages with massive I/O, which is something that the underlying execution and storage engine not good at. In fact, Hive strictly prohibit recursive references for CTEs and views. Hence the error you got.