SQL help - response (3) by todil

Dieter, I tried and iam getting this error. Failed 3504 I am getting selected non-aggregrated values must be part of associated group.
 
SELECT acct_id,
MRCH_NM,
EXTRACT(YEAR FROM trxn_post_dt) AS trans_year,
EXTRACT(MONTH FROM trxn_post_dt) AS trans_month,
trans_year * 12 + trans_month AS trans_ym,
SUM(SUM(trxn_amt))
OVER (PARTITION BY acct_id, MRCH_NM
ORDER BY trans_ym
ROWS 2 PRECEDING) AS sumamt
FROM POSTD_TRXN
GROUP BY 1,2,3
QUALIFY sumamt > 1000
AND trans_ym - MIN(trans_ym) OVER (PARTITION BY acct_id, MRCH_NM
ORDER BY trans_ym
ROWS 2 PRECEDING) = 2