# ALTER TABLE

A statement that changes the definition of an existing table.

## What is **ALTER TABLE** in a relational database?

**ALTER TABLE** — A statement that changes the definition of an existing table.

```sql
ALTER TABLE customer
ADD COLUMN phone_number CHARACTER VARYING(30);
```

Level: Apprentice · [More Database terms at this level](https://www.ask-codey.com/glossary/subjects/database/apprentice)

Updated: September 27, 2026

Source: https://www.ask-codey.com/glossary/alter-table