> ## Documentation Index
> Fetch the complete documentation index at: https://docs.regatta.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# ALTER TABLE

Modify existing table definitions.

## Synopsis

```
ALTER TABLE table_name
  action [, ... ]

where action is one of:
  SET READY
  ADD [ COLUMN ] column_name data_type [ column_constraint [ ... ] ] [ INDEX [ index_parameters ] ]

where column_constraint is:
{ NULL |
  NOT NULL |
  DEFAULT default_expr |
  UNIQUE |
  PRIMARY KEY |
  REFERENCES reftable [ (refcolumn) ] }

and index_parameters is:
WITH ( storage_parameter [= value] [, ... ] )
```

## Description

`ALTER TABLE` changes the metadata definition of an existing table in the current database.

The table must be in the `NOT READY` state, otherwise the command results in an error. A table is in `NOT READY` state if it’s created with the `CREATE TABLE SET NOT READY` option, and until the `ALTER TABLE SET READY` command is performed on it.

## Parameters

`table_name`

The name of an existing table to alter.

### `action`

`SET READY`

This form finalizes the table’s schema and index set, and makes it accessible for DML operations. Any subsequent ALTER TABLE command will fail as the table transitions to the READY state.

`ADD [ COLUMN ]`

Adds a new column to the table, using the same syntax as in [CREATE TABLE](/sql/ddl-commands/create-table). The column name must be unique within the table and conform with the [Identifiers Limitations](/sql/appendices/indentifiers-limitations).

**`column_name`**

The name of the added column.

**`data_type`**

Data type of the new column. For more information on the supported data types, refer to [Data Types](/sql/data-types).

The rest of the parameters used in this command are described in the [CREATE TABLE](/sql/ddl-commands/create-table) command.

## Examples

***

**Create a table as not ready and alter it to modify its definition:**

```sql theme={null}
CREATE TABLE SET NOT READY parts WITH (devices = (m1d2, m2d5, m3d3));

ALTER TABLE parts
  ADD COLUMN p_partkey INT PRIMARY KEY INDEX WITH (devices = (m1d2)),
  ADD COLUMN p_name VARCHAR(40) NOT NULL UNIQUE INDEX
    WITH (devices = (m1d2, m2d5, m3d3), range_separators = ('j', 'p'));

ALTER TABLE parts
  ADD COLUMN p_date DATE NOT NULL ;

ALTER TABLE parts SET READY;
```

This example creates a table and builds it gradually with `ALTER TABLE` commands, and eventually finalizes it with `SET READY`.

Note that the `ALTER TABLE` command can only work as long as the parts table is defined as `NOT READY`.

## Compatibility

The `ALTER TABLE` command conforms to the SQL standard, with exceptions listed below.

1. `SET READY` is a Regatta extension
2. `WITH` clause is a Regatta extension; storage parameters are not in the standard.