# Update data

UPDATE changes existing rows selected by WHERE. Expressions can read the old row values, so an assignment can increment or decrement a stored amount.

The resulting values are checked against declared types and constraints. Changes complete synchronously and can be grouped in a transaction.

## Example

```sql
CREATE TABLE stock(id INTEGER PRIMARY KEY, quantity INTEGER);
INSERT INTO stock VALUES (1, 5);
```

```sql
UPDATE stock
SET quantity = quantity - 1
WHERE id = 1
RETURNING id, quantity
FORMAT csv;
```

```text
1,4
```

Without WHERE, an update changes every row. RETURNING exposes the updated values.

## Upsert

Use `INSERT ... ON CONFLICT ... DO UPDATE` when the operation should insert a new row or update an existing conflicting row. This is separate from an ordinary UPDATE, which never inserts a missing row.

See [`UPDATE`](https://coordinatordb.com/docs/reference/statements/update), [`INSERT INTO`](https://coordinatordb.com/docs/reference/statements/insert-into) and [transactions](https://coordinatordb.com/docs/concepts/features/operations/insert/transactions).