问在Hive SQL中选择prev值

EN

SELECT user_, prev
FROM (SELECT *, ROW_NUMBER() OVER(PARTITION BY user_ ORDER BY ts) AS rn
      FROM (SELECT *, CASE 
                WHEN isnumber = 'y' THEN NULL
                WHEN LAG(isnumber,1) OVER(PARTITION BY user_ ORDER BY ts) = 'y'
                     THEN LAG(col,1) OVER(PARTITION BY user_ ORDER BY ts)
               END AS prev
             FROM tab) sub
    WHERE prev IS NOT NULL) sub2
WHERE rn = 1;