# UNION — MySQL Fundamentals: SQL, Joins and Transactions

Source: https://www.skillbyai.com/en/mysql/sql-union

> Stack results from several SELECT statements with UNION and UNION ALL and choose between deduplication and speed.

## Combining result sets

`UNION` stacks rows from two queries with the same column count, removing duplicates. `UNION ALL` keeps duplicates and is faster.

```sql
SELECT name FROM customers WHERE id = 1
UNION
SELECT name FROM customers WHERE id = 2;
```

Output:

```
name
Asha Rao
Rahul Mehta
```

**Quiz:** What's the key difference between UNION and UNION ALL?

- [ ] UNION ALL sorts the results
- [ ] They require the same table name
- [x] UNION removes duplicate rows, UNION ALL keeps them
- [ ] UNION is only for numbers

*Answer:* UNION removes duplicate rows, UNION ALL keeps them. UNION dedupes (extra work); UNION ALL doesn't, so it's faster.