Can I use… over(… exclude ties)

Exclude group removes all but the current row with the same order by-values as the current row from the selection of the frame.

SELECT SUM(x) OVER(ORDER BY val … EXCLUDE TIES)
  FROM …

Related

• Other frame exclude options: no-others, current row, group

• Tutorial: Window Frame Exclusion

• Other forms: window clause

Normative References

The exclude clause in window definitions—both, in over and window clauses—is defined in ISO/IEC 9075:2016-2 as part of optional feature T612, “Advanced OLAP operations”.