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

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maxMap

Syntax: maxMap(key, value) or maxMap(Tuple(key, value))

Calculates the maximum from value array according to the keys specified in the ‘key’ array. Passing tuple of keys and values arrays is synonymical to passing two arrays of keys and values. The number of elements in ‘key’ and ‘value’ must be the same for each row that is totaled. Returns a tuple of two arrays: keys in sorted order, and values calculated for the corresponding keys.

Example:

SELECT maxMap(a, b)
FROM values('a Array(Int32), b Array(Int64)', ([1, 2], [2, 2]), ([2, 3], [1, 1]))

┌─maxMap(a, b)──────┐
│ ([1,2,3],[2,2,1]) │
└───────────────────┘