APPROX_DISTINCT() OVER ...

All functions > WINDOW FUNCTION > APPROX_DISTINCT() OVER ...

Returns the approximate number of distinct values in the window frame.

Syntax

Diagram(
  Sequence(
    Terminal("APPROX_DISTINCT"),
    Terminal("("),NonTerminal('expr'),Terminal(")"),
    Terminal("OVER"),
    Terminal("("),
    NonTerminal("over_clause"),
    Terminal(")"),
  )
)

Parameter	Type	Required	Description
`expr`	`EXPRESSION`	Yes	Expression to count distinct values of
`over_clause`	`OVER CLAUSE`	Yes	OVER (PARTITION BY ... ORDER BY ... [FRAME ...])

Notes

Returns approximate count of distinct values using HyperLogLog algorithm
Much faster than exact COUNT(DISTINCT) for large datasets
Typical error rate around 2.3%
Always returns BIGINT type

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Last update at: 2026/03/03 16:47:38

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Syntax Notes