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

slug	sidebar_position	title
/en/sql-reference/aggregate-functions/reference/maxintersections	360	maxIntersections

maxIntersections

Aggregate function that calculates the maximum number of times that a group of intervals intersects each other (if all the intervals intersect at least once).

The syntax is:

maxIntersections(start_column, end_column)

Arguments

• start_column – the numeric column that represents the start of each interval. If start_column is NULL or 0 then the interval will be skipped.

• end_column - the numeric column that represents the end of each interval. If end_column is NULL or 0 then the interval will be skipped.

Returned value

Returns the maximum number of intersected intervals.

Example

CREATE TABLE my_events (
    start UInt32,
    end UInt32
)
Engine = MergeTree
ORDER BY tuple();

INSERT INTO my_events VALUES
   (1, 3),
   (1, 6),
   (2, 5),
   (3, 7);

The intervals look like the following:

1 - 3
1 - - - - 6
  2 - - 5
    3 - - - 7

Three of these intervals have a common value (the value is 4, but the value that is common is not important, we are measuring the count of the intersections). The intervals (1,3) and (3,7) share an endpoint but are not considered intersecting by the maxIntersections function.

SELECT maxIntersections(start, end) FROM my_events;

Response:

3

If you have multiple occurrences of the maximum interval, you can use the maxIntersectionsPosition function to locate the number and location of those occurrences.