# first_value

Returns the first value in the current ordered window frame. The function selects a row position; it retains a `NULL` at that position.

Frame bounds determine which rows can be selected. Use an explicit frame when the result should cover a fixed preceding range or the whole partition.

**Syntax**

```text
first_value(value) OVER (
    [PARTITION BY expression, ...]
    ORDER BY expression, ...
    [ROWS | RANGE | GROUPS frame_bounds]
)
```

**Arguments**

* `value` — The expression evaluated at the selected row.

**Returned value**
The selected input value, preserving its native type. An empty frame returns `NULL`. Frame exclusions apply before selecting the position.

**Examples**
**Reading from a growing frame**

The frame starts at the first sale and ends at the current row:

```sql
CREATE TABLE sales (day INTEGER, amount INTEGER);
INSERT INTO sales VALUES (1, 120), (2, 150), (3, 90);
```

```sql
SELECT day, amount,
       first_value(amount) OVER (
           ORDER BY day
           ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
       ) AS selected_amount
FROM sales
ORDER BY day
FORMAT csv;
```

```text
1,120,120
2,150,120
3,90,120
```

**Preserving NULL at the selected position**

```sql
CREATE TABLE readings (day INTEGER, value INTEGER);
INSERT INTO readings VALUES (1, NULL), (2, 20);
```

```sql
SELECT day, first_value(value) OVER (ORDER BY day)
FROM readings
ORDER BY day
FORMAT csv;
```

```text
1,\N
2,\N
```

See [window functions](https://coordinatordb.com/docs/reference/functions/window-functions) for supported frame units and exclusions.