ClickHouse/docs/en/sql-reference/aggregate-functions/reference/deltasum.md

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deltaSum

Syntax: deltaSum(value)

Adds the differences between consecutive rows. If the difference is negative, it is ignored. value must be some integer or floating point type.

Example:

select deltaSum(arrayJoin([1, 2, 3]));                  -- => 2
select deltaSum(arrayJoin([1, 2, 3, 0, 3, 4, 2, 3]));   -- => 7
select deltaSum(arrayJoin([2.25, 3, 4.5])); -- => 2.25