hive query to map keys to multiple values

Question

I have a table with a structure similar to the one below:

|C1|C2|C3|
|K1|V1|??|
|K1|V2|??|
|K1|V3|??|
|K2|V2|??|

I need to write a query that checks if the key(lets say K1) maps to a specific value in any row (say V2). If it does the value in column C3 is taken as 1 otherwise its 0.

I'd appreciate any help.

Answer 1

The folloiwng query should give the results you want. The subquery identifies all C1 values which map to a certain value in C2 at least once. If so, then we render the C3 values as 1, otherwise we show 0.

SELECT
    t1.C1,
    t1.C2,
    CASE WHEN t2.C1 IS NOT NULL THEN 1 ELSE 0 END AS C3
FROM yourTable t1
LEFT JOIN
(
    SELECT C1
    FROM yourTable
    GROUP BY C1
    HAVING SUM(CASE WHEN C2 = 'V1' THEN 1 ELSE 0 END) > 0
) t2
    ON t1.C1 = t2.C1