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

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quantile

Computes an approximate quantile of a numeric data sequence.

This function applies reservoir sampling with a reservoir size up to 8192 and a random number generator for sampling. The result is non-deterministic. To get an exact quantile, use the quantileExact function.

When using multiple quantile* functions with different levels in a query, the internal states are not combined (that is, the query works less efficiently than it could). In this case, use the quantiles function.

Syntax

quantile(level)(expr)

Alias: median.

Parameters

• level — Level of quantile. Optional parameter. Constant floating-point number from 0 to 1. We recommend using a level value in the range of [0.01, 0.99]. Default value: 0.5. At level=0.5 the function calculates median.
• expr — Expression over the column values resulting in numeric data types, Date or DateTime.

Returned value

• Approximate quantile of the specified level.

Type:

• Float64 for numeric data type input.
• Date if input values have the Date type.
• DateTime if input values have the DateTime type.

Example

Input table:

┌─val─┐
│   1 │
│   1 │
│   2 │
│   3 │
└─────┘

Query:

SELECT quantile(val) FROM t

Result:

┌─quantile(val)─┐
│           1.5 │
└───────────────┘

See Also

• median
• quantiles