---
title: "ALTER EXTERNAL TABLE"
source: https://cloudberry.apache.org/docs/sql-stmts/alter-external-table
---

# ALTER EXTERNAL TABLE

Changes the definition of an external table.

## Synopsis

```sql
ALTER EXTERNAL TABLE <name> <action> [, ... ]
```

where action is one of:

```sql
  ADD [COLUMN] <new_column> <type>
  DROP [COLUMN] <column> [RESTRICT|CASCADE]
  ALTER [COLUMN] <column> TYPE <type>
  OWNER TO <new_owner>
```

## Description

`ALTER EXTERNAL TABLE` changes the definition of an existing external table. These are the supported `ALTER EXTERNAL TABLE` actions:

- **ADD COLUMN** — Adds a new column to the external table definition.
- **DROP COLUMN** — Drops a column from the external table definition. If you drop readable external table columns, it only changes the table definition in Apache Cloudberry. The `CASCADE` keyword is required if anything outside the table depends on the column, such as a view that references the column.
- **ALTER COLUMN TYPE** — Changes the data type of a table column.
- **OWNER** — Changes the owner of the external table to the specified user.

Use the [ALTER TABLE](/docs/sql-stmts/alter-table.md) command to perform these actions on an external table:

- Set (change) the table schema.
- Rename the table.
- Rename a table column.
- Set (change) the distribution policy (writable external table only).

You must own the external table to use `ALTER EXTERNAL TABLE` or `ALTER TABLE`. To change the schema of an external table, you must also have `CREATE` privilege on the new schema. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have `CREATE` privilege on the external table's schema. A superuser has these privileges automatically.

Changes that you make to an external table definition with either `ALTER EXTERNAL TABLE` or `ALTER TABLE` do not affect the external data.

The `ALTER EXTERNAL TABLE` and `ALTER TABLE` commands cannot modify the type of the external table (read, write, web), the table `FORMAT` information, or the location of the external data. To modify this information, you must drop and recreate the external table definition.

## Parameters

**`name`**

The name (possibly schema-qualified) of an existing external table definition to alter.

**`column`**

Name of an existing column.

**`new_column`**

Name of a new column.

**`type`**

Data type of the new column, or new data type for an existing column.

**`new_owner`**

The role name of the new owner of the external table.

**`CASCADE`**

Automatically drop objects that depend on the dropped column, such as a view that references the column.

**`RESTRICT`**

Refuse to drop the column or constraint if there are any dependent objects. This is the default behavior.

## Examples

Add a new column to an external table definition:

```sql
ALTER EXTERNAL TABLE ext_expenses ADD COLUMN manager text;
```

Change the owner of an external table:

```sql
ALTER EXTERNAL TABLE ext_data OWNER TO jojo;
```

Change the data type of an external table:

```sql
ALTER EXTERNAL TABLE ext_leads ALTER COLUMN acct_code TYPE integer;
```

## Compatibility

`ALTER EXTERNAL TABLE` is a Apache Cloudberry extension. There is no `ALTER EXTERNAL TABLE` statement in the SQL standard or regular PostgreSQL.

## See also

[CREATE EXTERNAL TABLE](/docs/sql-stmts/create-external-table.md), [DROP EXTERNAL TABLE](/docs/sql-stmts/drop-external-table.md), [ALTER TABLE](/docs/sql-stmts/alter-table.md)