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minMap

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Description

The Map combinator can be applied to the min function to calculate the minimum value in a Map according to each key, using the minMap aggregate combinator function.

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Example usage

In this example, we’ll create a table that stores status codes and their counts for different timeslots, where each row contains a Map of status codes to their corresponding counts. We’ll use minMap to find the minimum count for each status code within each timeslot.
Query
CREATE TABLE metrics(
    date Date,
    timeslot DateTime,
    status Map(String, UInt64)
) ENGINE = MergeTree
ORDER BY ();

INSERT INTO metrics VALUES
    ('2000-01-01', '2000-01-01 00:00:00', (['a', 'b', 'c'], [15, 25, 35])),
    ('2000-01-01', '2000-01-01 00:00:00', (['c', 'd', 'e'], [45, 55, 65])),
    ('2000-01-01', '2000-01-01 00:01:00', (['d', 'e', 'f'], [75, 85, 95])),
    ('2000-01-01', '2000-01-01 00:01:00', (['f', 'g', 'g'], [105, 115, 125]));

SELECT
    timeslot,
    minMap(status),
FROM metrics
GROUP BY timeslot;
The minMap function will find the minimum count for each status code within each timeslot. For example:
  • In timeslot ‘2000-01-01 00:00:00’:
    • Status ‘a’: 15
    • Status ‘b’: 25
    • Status ‘c’: min(35, 45) = 35
    • Status ‘d’: 55
    • Status ‘e’: 65
  • In timeslot ‘2000-01-01 00:01:00’:
    • Status ‘d’: 75
    • Status ‘e’: 85
    • Status ‘f’: min(95, 105) = 95
    • Status ‘g’: min(115, 125) = 115
Response
   ┌────────────timeslot─┬─minMap(status)───────────────────────┐
1. │ 2000-01-01 00:01:00 │ {'d':75,'e':85,'f':95,'g':115}       │
2. │ 2000-01-01 00:00:00 │ {'a':15,'b':25,'c':35,'d':55,'e':65} │
   └─────────────────────┴──────────────────────────────────────┘

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See also