# Connect an existing source

Make an existing database, warehouse, or object-storage dataset queryable in Altertable. An external catalog reads data from its source without importing it into managed tables.

You need connection credentials and permission to add a catalog. If the source restricts network access, configure [network access](/docs/administration/network.md) first.

## 1. Choose the source

Open [Connect existing data](/docs/lakehouse/external-catalogs.md) and choose the guide for your database, warehouse, or table format. Follow that guide to create the catalog in the intended environment.

For object storage, distinguish [querying files in place](/docs/lakehouse/query/object-storage.md) from [syncing files into managed tables](/docs/lakehouse/ingest/object-storage.md).

## 2. Inspect a table

Open **Catalogs** and find the new catalog. Inspect its schemas and tables, then open [SQL Explorer](/docs/lakehouse/query/sql-explorer.md).

Replace the example catalog, schema, and table with names from your source:

```sql
SELECT * FROM my_source.public.my_table LIMIT 10;
```

## 3. Verify the result

Compare the returned rows with the source. Confirm that you connected the intended environment and that the source credentials expose the tables you need.

## Do this with your agent

```text
Read https://altertable.ai/docs/getting-started/connect-data.md. Help me connect an existing source to Altertable. Inspect project configuration without reading secret files and ask only for the source, target environment, or network constraints you cannot determine. Follow the matching supported connection guide and explain the required access and where the data stays. Confirm the catalog configuration before creating it. Then inspect the schemas and verify a bounded query against an agreed real table. Report the catalog, table, query, and any access or data gaps.
```

Next, [build a data app](/docs/data-apps/build.md) with the data you connected.