---
title: "ALTER TABLE"
slug: "dev-database-reference-sql-alter-table"
updated: 2026-10-30T18:19:11Z
published: 2026-10-30T18:19:11Z
canonical: "docs.vastdata.com/dev-database-reference-sql-alter-table"
---

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

# ALTER TABLE

*Applies to VAST Cluster 5.5.*

Renames a table, adds, renames and drops columns, and adds a sort key.

## Syntax

```
ALTER TABLE "<bucket>/<schema>".<table> RENAME TO "<bucket>/<schema>.<new-table>"
ALTER TABLE "<bucket>/<schema>".<table> ADD [COLUMN] <column> <type>
ALTER TABLE "<bucket>/<schema>".<table> RENAME COLUMN <column> TO <new-column>
ALTER TABLE "<bucket>/<schema>".<table> DROP [COLUMN] <column>
ALTER TABLE "<bucket>/<schema>".<table> DROP [COLUMN] "<struct-column>.<field>"
ALTER TABLE "<bucket>/<schema>".<table> ADD CONSTRAINT <constraint-name> SORT KEY (<column> [, ...])
```

## Parameters and rules

| Form | Rules |
| --- | --- |
| `RENAME TO` | Give the new name as one quoted string, `&quot;&lt;bucket&gt;/&lt;schema&gt;.&lt;new-table&gt;&quot;`: bucket and schema, a dot, then the new table name. A bare new name, such as `RENAME TO new_name`, fails with `Invalid Argument`. |
| `ADD [COLUMN]` | Adds a column of any [type](/develop/docs/dev-database-reference-sql-data-types), including a struct or a list. Existing rows get NULL in it. |
| `RENAME COLUMN` | Renames a top-level column. |
| `DROP [COLUMN]` | Drops a column. To drop one field of a struct column, quote the dotted name: `DROP COLUMN &quot;location.alt&quot;`. |
| `ADD CONSTRAINT ... SORT KEY` | Adds a sort key to a table that has none, and so makes it a sorted table. The table can already hold rows; they're sorted in the background ([Sorted tables](/docs-5-5/docs/sorted-tables)). Up to 4 columns. |

- You can't change a column's type or default: `ALTER COLUMN ... SET DATA TYPE` and `ALTER COLUMN ... SET DEFAULT` fail. To change a type, add a new column, copy the values into it with [UPDATE](/develop/docs/dev-database-reference-sql-update) and a `CAST`, then drop the old column.
- `ADD CONSTRAINT` accepts only `SORT KEY`. A `PRIMARY KEY` fails.
- A sort key can't be removed or changed once it's set, and some table structures can't be sorted, such as a table with a semi-sorted projection or user-defined row IDs. Check [limits](/develop/docs/dev-database-reference-limits#what-cant-be-changed-later) before you add one. [DESCRIBE](/develop/docs/dev-database-reference-sql-describe) doesn't show the sort key.
- On a vector-indexed table you can't add or drop columns, or rename the indexed column; see [vector search SQL](/develop/docs/dev-database-reference-sql-vector-search).
- The Query Engine can't alter a partitioned table; see [not supported](/develop/docs/dev-database-reference-sql-not-supported).

## What happens on the cluster

`ALTER TABLE` changes the table's definition in the database's catalog. Adding or dropping a column doesn't rewrite the existing rows ([write path](/develop/docs/dev-database-concepts-architecture-write-path#adding-and-dropping-columns)). Adding a sort key starts background sorting of the table's data on the cluster ([write path](/develop/docs/dev-database-concepts-architecture-write-path#sorted-tables)). Nothing is computed in the Query Engine.

## Example

The examples use the `run()` helper and the environment variables described in the [SQL reference](/develop/docs/dev-database-reference-sql-index#example-connect-and-use-a-transaction). This block connects, and creates the schema `docs_sql_alter_table` with a small table:

```
import os
import re

import adbc_driver_manager
import adbc_driver_manager.dbapi as dbapi
import adbc_driver_vastdb

BUCKET = os.environ["VASTDB_BUCKET"]
SCHEMA = f'"{BUCKET}/docs_sql_alter_table"'

def connect(autocommit=True):
    return dbapi.connect(
        driver=adbc_driver_vastdb.get_driver_path(),
        db_kwargs={
            "vast.db.endpoint": os.environ["QE_ENDPOINT"],
            "vast.db.access_key": os.environ["AWS_ACCESS_KEY_ID"],
            "vast.db.secret_key": os.environ["AWS_SECRET_ACCESS_KEY"],
        },
        autocommit=autocommit,
    )

def server_message(e):
    """The server's message in a driver error, without the request ID or the echoed statement."""
    text = re.sub(r"\[req=0x[0-9a-f]+\]: ", "", str(e))
    found = (re.search(r'message: "(.*?)", request_id', text, re.S)
             or re.search(r"description: (.*)\)", text, re.S))
    message = found.group(1) if found else text.strip().splitlines()[-1]
    message = re.sub(r"^Plan query: '.*?' failed with: ", "", message, flags=re.S)
    message = re.split(r"\\n|\n", message)[0].replace('\\"', '"')
    return message.replace(BUCKET, "<bucket>")

def run(sql):
    """Run one statement. Print the rows it returns, or the error."""
    try:
        with conn.cursor() as cur:
            cur.execute(sql)
            rows = cur.fetchall() if cur.description else []
    except (adbc_driver_manager.Error, OSError) as e:
        print(f"{type(e).__name__}: {server_message(e)}")
    else:
        print(rows)

conn = connect()
run(f"CREATE SCHEMA IF NOT EXISTS {SCHEMA}")
run(f"CREATE TABLE IF NOT EXISTS {SCHEMA}.readings (id BIGINT, city VARCHAR)")
run(f"INSERT INTO {SCHEMA}.readings VALUES (1, 'Lisbon'), (2, 'Oslo')")
```

```
[]
[]
[(2,)]
```

Add a column, rename it, and drop it again:

```
run(f"ALTER TABLE {SCHEMA}.readings ADD COLUMN temp INTEGER")
run(f"ALTER TABLE {SCHEMA}.readings RENAME COLUMN temp TO temperature")
run(f"SELECT id, city, temperature FROM {SCHEMA}.readings ORDER BY id LIMIT 10")
run(f"ALTER TABLE {SCHEMA}.readings DROP COLUMN temperature")
```

```
[]
[]
[(1, 'Lisbon', None), (2, 'Oslo', None)]
[]
```

Add a struct column, drop one of its fields, and look at the result:

```
run(f"ALTER TABLE {SCHEMA}.readings ADD COLUMN location STRUCT(lat DOUBLE, lon DOUBLE, alt DOUBLE)")
run(f'ALTER TABLE {SCHEMA}.readings DROP COLUMN "location.alt"')
run(f"DESCRIBE {SCHEMA}.readings")
```

```
[]
[]
[('id', 'BIGINT', 'YES', None, None, None), ('city', 'VARCHAR', 'YES', None, None, None), ('location', 'STRUCT(lat DOUBLE, lon DOUBLE)', 'YES', None, None, None)]
```

Rename the table. The bare name fails; the full name in one quoted string works:

```
run(f"ALTER TABLE {SCHEMA}.readings RENAME TO readings_2026")
run(f'ALTER TABLE {SCHEMA}.readings RENAME TO "{BUCKET}/docs_sql_alter_table.readings_2026"')
run(f"SELECT count(*) FROM {SCHEMA}.readings_2026")
```

```
InternalError: internal error: Invalid Argument
[]
[(2,)]
```

Add a sort key to the populated table. Changing a column's type fails:

```
run(f"ALTER TABLE {SCHEMA}.readings_2026 ADD CONSTRAINT readings_sk SORT KEY (id)")
run(f"ALTER TABLE {SCHEMA}.readings_2026 ALTER COLUMN city SET DATA TYPE VARCHAR")
```

```
[]
InternalError: internal error: This functionality is not implemented yet (specific message not set)
```

Clean up:

```
run(f"DROP TABLE IF EXISTS {SCHEMA}.readings_2026")
run(f"DROP TABLE IF EXISTS {SCHEMA}.readings")
run(f"DROP SCHEMA IF EXISTS {SCHEMA}")
conn.close()
```

```
[]
[]
[]
```

## Errors

The class is `InternalError`.

| You wrote | Message |
| --- | --- |
| `RENAME TO &lt;bare-name&gt;` | `internal error: Invalid Argument` (status 20) |
| `ALTER COLUMN ... SET DATA TYPE` or `SET DEFAULT` | `internal error: This functionality is not implemented yet (specific message not set)` (status 58) |
| `ADD CONSTRAINT ... PRIMARY KEY` | `Not implemented Error: BindAlterAddIndex not supported by this catalog` |

On a vector-indexed table, `ADD COLUMN` and `DROP COLUMN` fail with `Invalid Argument`, and renaming the indexed column fails with `Tried to drop a column which cannot be dropped` ([vector search SQL](/develop/docs/dev-vector-search-reference-sql#changing-data-dml)).

## Trino and Spark

Trino and Spark alter tables with their own statements; in Trino, sorting is a table property. See [Trino](/develop/docs/dev-database-integrations-trino#sorted-tables) and [Spark](/develop/docs/dev-database-integrations-spark#sorted-tables), where sorting from Spark is still unconfirmed.

See also: [CREATE TABLE](/develop/docs/dev-database-reference-sql-create-table), [limits](/develop/docs/dev-database-reference-limits), [schema changes in the ingest guide](/develop/docs/dev-database-guides-ingest#when-incoming-data-has-new-columns).