If such two transactions run concurrently, a write skew anomaly occurs, and the result of order_summary refreshed in T1 will not contain the record inserted in T2.
Indeed we have write skew anomaly here between the two transactions.
On the other hand, if the materialized view participates in predicate locking and the transaction isolation level is SELIALIZABLE, this anomaly can be avoided; one of the transaction will be aborted and suggested to be retried.
