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javier merged 2 commits into from
Feb 26, 2026
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Document count(distinct) syntax #379

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3dfe9ea
Document count(distinct column_name) syntax in aggregation reference
javier Feb 26, 2026
1cc5c2a
Add backwards-compatibility note to count_distinct
javier Feb 26, 2026
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23 changes: 23 additions & 0 deletions documentation/query/functions/aggregation.md
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Expand Up @@ -703,6 +703,9 @@ SELECT payment_type, corr(price, quantity) FROM transactions GROUP BY payment_ty
- `count()` or `count(*)` - counts the number of rows irrespective of underlying
data.
- `count(column_name)` - counts the number of non-NULL values in a given column.
- `count(distinct column_name)` - counts the number of distinct non-NULL values
in a given column. This is identical to
[`count_distinct(column_name)`](#count_distinct).
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#### Parameters

Expand Down Expand Up @@ -774,9 +777,22 @@ SELECT payment_type, count(amount) FROM transactions;
| card | 67 |
| NULL | 4 |

Count distinct values using standard SQL syntax (identical to `count_distinct`):

```questdb-sql
SELECT payment_type, count(distinct counterparty) FROM transactions;
```

| payment_type | count |
| :----------- | :---- |
| cash | 3 |
| card | 23 |
| NULL | 5 |

:::note

`NULL` values are aggregated with `count()`, but not with `count(column_name)`
or `count(distinct column_name)`.

:::

Expand All @@ -790,6 +806,13 @@ SELECT payment_type, count(amount) FROM transactions;
`count_distinct(column_name)` - counts distinct non-`NULL` values in `varchar`,
`symbol`, `long256`, `UUID`, `IPv4`, `long`, `int` or `string` columns.

:::tip

`count_distinct` is available for backwards compatibility. We recommend using
the standard SQL syntax [`count(distinct column_name)`](#count) instead.

:::

#### Return value

Return value type is `long`.
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