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

# Schema monitor

> Schema changes and SQL definition changes are tracked automatically for every warehouse table and view. Set up a schema change alert to be notified about them.

The schema monitor tracks the columns of your warehouse tables and views and records every change to them. It works differently from the other monitor types:

* **There is nothing to set up.** Schema changes are tracked for every table and view in your connected data warehouses. That is why `Schema` is not offered under **Add monitor** on an asset, and it does not count toward your monitor limit.
* **It never notifies anyone on its own.** Changes are recorded on the asset, and you are notified only when a [schema change alert](#getting-notified-about-schema-changes) covers that asset.
* **It never raises an issue.** A schema change is a record of what changed, not a failure, so it does not appear in **Issues** and does not change an asset's health.

## What is detected

Each time Coalesce Quality refreshes the catalog of your data warehouse (every four hours by default), it compares the columns of every table and view with the previous refresh and records:

* **Column added**
* **Column removed**
* **Column type changed**, with the previous and the current type

Columns are matched by name, so a renamed column is recorded as one column removed and one column added. The first refresh of a new table only records its columns as the starting point, so a newly created table never shows up as a change.

Tables built by dbt, SQLMesh or Coalesce Transform are covered through the warehouse table or view they build, and the model's own page shows those changes too.

### SQL definition changes

Coalesce Quality also records when the SQL that defines an asset changes, for example the definition of a view, and keeps a diff of the old and new SQL. SQL definition changes are only recorded. They do not trigger alerts.

## Where to see schema changes

Open the asset in the catalog and select the **Changes** tab. It lists the commits, schema changes and SQL definition changes on the asset for the last 30 days by default. Use the **Type** filter to narrow it to **Schema changes** or **SQL definition changes**, and the date range to look further back.

Select a change to open its details:

* **Schema change**—each changed column, marked **Add**, **Remove** or **Type change**, with its type. A type change shows the previous and the current type.
* **SQL definition change**—a diff of the previous and the current SQL.

Each change is also recorded as a run in the asset's **Logs** tab, under the run types **Schema Change** and **SQL Change**.

## Getting notified about schema changes

To be notified when a schema changes, create a schema change alert:

1. Go to **Settings → Alerts**, and under **Asset alerts** click **Add alert**.
2. Under **Alert type**, select **Schema change**, then select the assets the alert covers.
3. Choose the alert settings:
   * **Notify about upstream changes**—also alert on schema changes in assets upstream of the ones you selected.
   * **Schedule digest**—turn on **Enable daily digest** to get one summary per day at a time you choose (UTC), instead of one alert per change.
4. Choose where the alert is sent. Schema change alerts can go to Slack, Microsoft Teams and email.

The alert lists the columns that were added, removed, or changed type. It fires on every schema change on the selected assets, so narrow the asset selection if you only want alerts for some of them.

See [Setting up alerts](/alerts/setting-up-alerts) and [Routing alerts](/alerts/routing-alerts) for the other alert options.

## Schema changes in issue triage

When [Scout](/scout/scout) triages an issue, it checks for schema changes on the affected asset and on the assets upstream of it in the days before the issue started, because an upstream column change often explains a failing test or monitor. This works whether or not a schema change alert is set up.


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