lancedb/docs/web/sql/ddl.mdx

---
title: "DDL"
sidebarTitle: "DDL"
description: "Creating and altering catalog objects: tables, views, indexes, functions, and columns."
icon: pen-ruler
keywords: ["ddl", "create table", "alter table", "add column", "create function", "create index", "wal"]
---

<Badge color="red">Enterprise</Badge> [SQL runs on a deployment.](/sql)

Statements that change what exists rather than what it holds. For the values in
a table, see [DML](/sql/dml).

## Tables {#tables}

```sql
CREATE TABLE documents (id BIGINT, title VARCHAR, created_at TIMESTAMP)
CREATE TABLE recent AS SELECT * FROM documents WHERE created_at > now() - INTERVAL '7 days'
DROP TABLE documents
```

Column types are Arrow types under SQL names -- see
[Data types](/sql/data-types). A table in a [namespace](/namespaces) is written
as a dotted path: `prod.events.clicks`.

## Views {#views}

```sql
CREATE VIEW recent_matches AS
SELECT t1.floats FROM documents AS t1
INNER JOIN categories AS t2 ON t1.ints = t2.ints

DROP VIEW recent_matches
```

`CREATE VIEW` returns the view's schema -- column name, type, nullability --
resolved from the query at creation time. A view stores only the query; see
[Views](/management/view).

## Columns {#columns}

`ALTER TABLE ... ADD COLUMN` covers three different things, distinguished by
what follows the column name.

### A plain column {#plain-column}

```sql
ALTER TABLE t ADD COLUMN c INT
```

Added empty and nullable. Nothing is computed.

### A computed column {#computed-column}

```sql
ALTER TABLE t ADD COLUMN doubled AS value * 2
```

`AS <expression>` declares a [computed column](/feature-engineering/add-computed-column).
The column is committed empty and the expression is stored, not evaluated --
declaring one on a billion-row table costs what declaring one on an empty table
costs. [`REFRESH COLUMN`](/sql/refresh) fills it.

### A function column {#function-column}

```sql
ALTER TABLE t ADD COLUMN embedded AS embed(name) WITH (version = 'fv_1')
```

When the expression calls a [registered function](#functions), the column is
filled by running that function on workers. `version` pins which immutable
function version fills it, so a later registration does not silently change what
the column means.

Several modifiers narrow what gets computed:

| | |
| --- | --- |
| `FILTER (WHERE pred)` | only rows matching `pred` are computed |
| `IGNORE NULLS` | rows with null inputs are skipped |
| `OVER (PARTITION BY col)` | the function sees rows grouped by `col` |

A function returning several values fills several columns at once:

```sql
ALTER TABLE t ADD COLUMN (label, score) AS classify(text) WITH (version = 'fv_1')
```

```sql
ALTER TABLE t ADD COLUMN c AS f(x) FILTER (WHERE keep) WITH (version = 'fv_1')
ALTER TABLE t ADD COLUMN c AS f(x) WITH (num_workers = '2')
```

<Note>
`WITH` on a plain computed column accepts only `version`. Resource options such
as `num_workers` apply to function columns, where there are workers to size.
</Note>

## Functions {#functions}

```sql
CREATE FUNCTION f(x BIGINT) RETURNS BIGINT
LANGUAGE python
AS 'def f(x): return x * 2'
WITH (pip = 'numpy==1.26.4', python_version = '3.11')
```

The body is Python source. Its dependencies are declared with it and are part of
the **immutable function version** -- changing one produces a new version rather
than altering the registered one, so a column filled by an earlier version is
unaffected.

| Option | |
| --- | --- |
| `pip` | pip requirements for the worker environment |
| `conda` | conda packages instead of pip |
| `conda_channels` | channels in priority order; requires `conda` |
| `python_version` | worker Python version, defaulting to yours |
| `gpu` | `'true'` when every execution needs a GPU |

**Errors and limits**

| | |
| --- | --- |
| `LANGUAGE` other than `python` | refused |
| `pip` and `conda` together | refused -- pick one |
| `conda_channels` without `conda` | refused |
| `gpu` set to anything but `'true'` | refused |
| An empty body | refused |
| Any other option | refused, and the message lists what is supported |

See [Functions](/management/function) for the SDK equivalent and for diagnosing
environment mismatches.

## Indexes {#indexes}

```sql
CREATE INDEX ON documents (title)
DROP INDEX documents.title_idx
```

<Note>
SQL `CREATE INDEX` covers **one column** and takes **no user-chosen name** --
the server names it. For a multi-column or named index, use the SDK. `DROP
INDEX` takes the qualified `table.index` name; find it with `list_indices`.
</Note>

Index type and parameters are chosen in the SDK; see [Indexing](/indexing).

## Table properties {#properties}

```sql
ALTER TABLE t SET UNENFORCED PRIMARY KEY (id)
```

Records which column identifies a row. **Unenforced** is not a hedge in the
naming: uniqueness is not checked on write, and declaring it does not make
duplicates impossible. It tells the planner what to assume.

```sql
ALTER TABLE t SET WAL
ALTER TABLE t SET WAL WITH (sharding = 'bucket', buckets = 4)
ALTER TABLE t SET WAL WITH (maintained_indexes = '')
ALTER TABLE t UNSET WAL
```

A write-ahead log makes small frequent writes cheap by batching them out of the
commit path. `sharding` and `buckets` spread the log so concurrent writers do
not contend on one place; `maintained_indexes` chooses which indexes are kept
current against WAL rows.

<Warning>
[`TABLESAMPLE`](/sql/sampling) is refused on a WAL-backed table, because rows a
sample would draw from are not all in the fragments yet.
</Warning>

## See also {#see-also}

<CardGroup cols={2}>
  <Card title="DML" icon="pen-to-square" href="/sql/dml">
    Changing rows rather than structure.
  </Card>
  <Card title="Refresh" icon="arrows-rotate" href="/sql/refresh">
    Filling the columns declared here.
  </Card>
  <Card title="Management" icon="folder-tree" href="/management">
    The same operations from the SDKs.
  </Card>
  <Card title="SHOW" icon="list" href="/sql/show">
    Listing what exists.
  </Card>
</CardGroup>