# regr_count

Counts input pairs for which both numeric arguments are non-`NULL`. Use it to find the number of observations admitted by the covariance, correlation and regression aggregates.

**Syntax**

```text
regr_count(y, x)
```

**Arguments**

* `y` — The dependent numeric variable.
* `x` — The independent numeric variable.

A row with either argument `NULL` is excluded. Nonfinite numeric pairs are counted.

**Returned value**

A nonnegative `INTEGER` pair count. Empty input, or input with no complete pairs, returns `0`.

**Examples**

**Counting complete observations**

```sql
CREATE TABLE measurements (hour INTEGER, reading INTEGER);
INSERT INTO measurements VALUES (1, 3), (2, 5), (3, NULL), (NULL, 9);
```

```sql
SELECT count(*) AS rows,
       count(hour) AS hours,
       count(reading) AS readings,
       regr_count(reading, hour) AS complete_pairs
FROM measurements
FORMAT csv;
```

```text
4,3,3,2
```

**No complete observations**

```sql
CREATE TABLE incomplete_measurements (hour INTEGER, reading INTEGER);
INSERT INTO incomplete_measurements VALUES (1, NULL), (NULL, 5);
```

```sql
SELECT regr_count(reading, hour)
FROM incomplete_measurements
FORMAT csv;
```

```text
0
```

See [`regr_slope`](https://coordinatordb.com/docs/reference/functions/aggregate-functions/regr-slope), [`covar_pop`](https://coordinatordb.com/docs/reference/functions/aggregate-functions/covar-pop) and [`corr`](https://coordinatordb.com/docs/reference/functions/aggregate-functions/corr) for calculations over the admitted pairs.