APPROX_DISTINCT() OVER ...

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

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

Syntax

APPROX_DISTINCT(expr [, precision]) OVER ([PARTITION BY expr [, ...]] [ORDER BY sort_item [, ...]] [ROWS|RANGE|GROUPS frame])

APPROX_DISTINCT(expr [, precision]) OVER ([PARTITION BY expr [, ...]] [ORDER BY sort_item [, ...]] [ROWS|RANGE|GROUPS 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

See also

• OVER clause

Examples

SELECT
    f1 := ZIP(ARRAY[1, 2, 3, 4] AS id, ARRAY['a', 'b', 'b', 'c'] AS v).TRANSFORM(SELECT APPROX_DISTINCT(v) OVER (ORDER BY id ASC)).UNWRAP() -- Per-row approximate distinct counts (BIGINTs), not the VARCHAR values in v
;