# Evolve Iceberg table schema
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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)