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.

Note that for an empty numeric sequence, quantile will return NaN, but its quantile* variants will return either NaN or a default value for the sequence type, depending on the variant.

Syntax

quantile(level)(expr)

Alias: median.

Arguments

• 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