---
title: "Changes since a version"
sidebarTitle: "Changes"
description: "CHANGES: read the rows appended to a table since an earlier version."
icon: clock-rotate-left
keywords: ["changes", "append", "incremental", "cdc", "version"]
availability:
  embedded: unavailable
  enterprise: available
---

`CHANGES` reads the rows appended to a table since an earlier
[version](/management/table#versioning), without rescanning rows that were
already there:

<CodeGroup>
```sql SQL icon="database"
SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 42)
```
</CodeGroup>

This returns the rows appended after version 42, up to the table's current
version at the time the query runs.

## Strictly append-only {#strict}

The clause is named for what it requires, not just what it does: every
change to the table between the starting version and the current one must
be an append. If any of them inserted with changes other than a pure append
-- an update, a delete, a merge -- the query is refused rather than silently
returning an incomplete or wrong result. Re-run it with a later starting
version that is itself after the non-append write, or read the table in full
instead of incrementally.

`INFORMATION => APPEND_ONLY` is the only supported value: it names what kind
of history the clause is willing to read, not a choice among several. `AT
(VERSION => ...)` takes a positive integer; there is no `AT (TIMESTAMP =>
...)` form for this clause, unlike other version qualifiers.

## Where the clause can go {#placement}

It attaches to a table in `FROM`, including inside a subquery, a CTE, a join,
a set operation, or `EXPLAIN`:

<CodeGroup>
```sql SQL icon="database"
WITH recent AS (
  SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 42)
)
SELECT count(*) FROM recent

SELECT * FROM events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 10) a
JOIN events CHANGES (INFORMATION => APPEND_ONLY) AT (VERSION => 20) b
  ON a.id = b.id
```
</CodeGroup>

Each occurrence of a table keeps its own starting version, even when the same
table is referenced more than once in one statement.

## Unsupported forms {#refused}

| | |
| --- | --- |
| `CHANGES (INFORMATION => DEFAULT)` | only `APPEND_ONLY` is supported |
| `AT (TIMESTAMP => ...)` | only `AT (VERSION => ...)` is supported |
| `AT (VERSION => 0)` | the starting version must be positive |
| `... END (VERSION => ...)` | not supported; the current version is always the end |
| `CHANGES ... TABLESAMPLE (...)` | cannot be combined on the same table reference |

## What to read next {#next}

<CardGroup cols={2}>
  <Card title="Table" icon="table" href="/sql/ddl/table">
    CREATE, ALTER, CLONE and versioning basics.
  </Card>
  <Card title="Select" icon="magnifying-glass" href="/sql/dql/select">
    The rest of the query grammar this clause attaches to.
  </Card>
</CardGroup>