# UNION

UNION appends both inputs and removes duplicate complete rows. `UNION ALL` appends the inputs while retaining every duplicate.

## Syntax

```text
query UNION [ALL] query
[ORDER BY expression, ...]
[LIMIT count [OFFSET offset]]
```

Both inputs must return the same number of columns. Result column names come from the first query. Duplicate comparison applies to whole rows; `NULL` is equal to another `NULL` for this purpose.

A final `ORDER BY` or `LIMIT` applies to the combined result. Set operators at the same query level are evaluated from left to right. Put a nested query in a FROM subquery when a different grouping is needed.

## Example

### Combining two sets of identifiers

```sql
CREATE TABLE first_set (id INTEGER);
INSERT INTO first_set VALUES (1), (2);

CREATE TABLE second_set (id INTEGER);
INSERT INTO second_set VALUES (2), (3);
```

```sql
SELECT id FROM first_set
UNION
SELECT id FROM second_set
ORDER BY id
FORMAT csv;
```

```text
1
2
3
```

### Retaining duplicates

```sql
SELECT 1 AS id
UNION ALL
SELECT 1
FORMAT csv;
```

```text
1
1
```

See [`UNION`](https://coordinatordb.com/docs/reference/statements/select/union), [`INTERSECT`](https://coordinatordb.com/docs/reference/statements/select/intersect) and [`EXCEPT`](https://coordinatordb.com/docs/reference/statements/select/except) for the other set operations.