# `STDDEV/STDDEV_SAMP`

**Applies to:** ✅ Data 360 SQL ✅ Tableau Hyper API

Computes the sample standard deviation of input values.

## Syntax

```sql
stddev(<expression>)
```

## Arguments

### Required

- `<expression>`: An expression of any numerical type.

## Returns

- `NUMERIC(38,6)` for integer-type or numeric arguments.
- `double precision` for floating-point arguments.

Returns NULL if the computation is meaningless.

## Considerations

- Uses N-1 in the denominator (Bessel's correction).
- Use `STDDEV_POP` for population standard deviation.
- Cast the input to `double precision` to get a `double precision` result.

## Examples

### Calculate Standard Deviation

Find the standard deviation of prices.

```sql
SELECT stddev(price) AS price_stddev
FROM products;
```

### Standard Deviation by Group

Calculate standard deviation for each category.

```sql
SELECT category, stddev(price) AS price_stddev
FROM products
GROUP BY category;
```

### Force Double Precision Output

Cast to get a specific output type.

```sql
SELECT stddev(CAST(quantity AS double precision)) AS qty_stddev
FROM orders;
```

## Related Documentation

- [STDDEV_POP](/docs/data/data-cloud-query-guide/references/dc-sql-reference/stddev-pop.md)
- [STDDEV](/docs/data/data-cloud-query-guide/references/dc-sql-reference/stddev.md)
- [VARIANCE](/docs/data/data-cloud-query-guide/references/dc-sql-reference/variance.md)
- [Aggregate Functions](/docs/data/data-cloud-query-guide/references/dc-sql-reference/aggregate.md)