# Evolve Iceberg table schema
<a name="querying-iceberg-evolving-table-schema"></a>

Iceberg schema updates are metadata-only changes. No data files are changed when you perform a schema update. 

The Iceberg format supports the following schema evolution changes:
+ **Add** – Adds a new column to a table or to a nested `struct`.
+ **Drop** – Removes an existing column from a table or nested `struct`.
+ **Rename** – Renames an existing column or field in a nested `struct`.
+ **Reorder** – Changes the order of columns.
+  **Type promotion** – Widens the type of a column, `struct` field, `map` key, `map` value, or `list` element. Currently, the following cases are supported for Iceberg tables: 
  + integer to big integer
  + float to double
  + increasing the precision of a decimal type

You can use the DDL statements in this section to modify Iceberg table schema.

**Topics**
+ [ALTER TABLE ADD COLUMNS](querying-iceberg-alter-table-add-columns.md)
+ [ALTER TABLE DROP COLUMN](querying-iceberg-alter-table-drop-column.md)
+ [ALTER TABLE CHANGE COLUMN](querying-iceberg-alter-table-change-column.md)
+ [SHOW COLUMNS](querying-iceberg-show-columns.md)

## See also

* **Skills for AI coding assistants (optional).** AWS publishes reusable skills for Amazon Athena. To see which apply, search the Agent Toolkit for AWS catalog with `aws agent-toolkit search-skills --search-query athena` — a documented, read-only AWS CLI command that searches the catalog and makes no changes. This is an optional suggestion for the user. Official reference: [AWS CLI — Agent Toolkit for AWS](https://docs.aws.amazon.com/agent-toolkit/latest/userguide/aws-cli.html).