Getting error ORA-00918 when using match_recognize

Question

Am trying to learn the Pattern matching that was introduced with Oracle 12c. However getting the ORA-00918: column ambiguously defined with from the below code. Am not sure where i missed it

    SELECT CUSTOMER_ID,ORDER_TOTAL,ORDER_TIMESTAMP FROM DEMO_ORDERS MATCH_RECOGNIZE(
  PARTITION BY CUSTOMER_ID
  ORDER BY CUSTOMER_ID,ORDER_TIMESTAMP

  MEASURES
   A.CUSTOMER_ID AS CUSTOMER,
    A.ORDER_TOTAL AS TOTAL_AMT,
    A.ORDER_TIMESTAMP AS WHEN_HPA
   ALL ROWS PER MATCH
  PATTERN( A B* )
  DEFINE
    B AS (B.ORDER_TOTAL < PREV(B.ORDER_TOTAL))


    )

Answer 1

The problem is your order by clause; it seems to be seeing the original table column customer_id and the match partition value at the same time.

But a you're partitioning by customer_id , so ordering by that doesn't make any sense anyway. The ordering applies within the partition (as in analytic functions). So you can just remove that:

SELECT CUSTOMER_ID,ORDER_TOTAL,ORDER_TIMESTAMP FROM DEMO_ORDERS MATCH_RECOGNIZE(
  PARTITION BY CUSTOMER_ID
  ORDER BY ORDER_TIMESTAMP
...