POST_START
# Using the Catalog.Schema.Object Three-Level Namespace in Databricks Unity Catalog

## PRIMARY OPERATION: `USE CATALOG training;`

The Unity Catalog in Databricks provides a three-level namespace structure: `Catalog.Schema.Object`. This structure allows you to organize and manage your data assets in a hierarchical and secure manner.

The **primary operation** in this lesson is to **use the catalog** named `training`. This is the top-level namespace in the Unity Catalog hierarchy.

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## Step 1: Use the Training Catalog

To begin, you need to switch the current context to the `training` catalog. This is done using the following SQL command:

“`sql
USE CATALOG training;
“`

This command sets the default catalog for subsequent operations, such as querying tables or creating objects.

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## Step 2: Use the Sales Schema (Optional but Recommended)

After using the catalog, you may optionally switch to a schema within that catalog. For example, to use the `sales` schema:

“`sql
USE SCHEMA sales;
“`

This command sets the default schema for subsequent operations, making it easier to reference objects within that schema.

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## Step 3: Query the Customers Table

Now that you are in the `training` catalog, you can query objects within it. For example, to select all data from the `customers` table in the `sales` schema, you can use:

“`sql
SELECT * FROM sales.customers;
“`

This query retrieves all rows and columns from the `customers` table located in the `sales` schema of the `training` catalog.

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## Step 4: Query the Customers Table Using the Full Three-Level Namespace

Alternatively, you can reference the `customers` table using the full three-level namespace directly, without switching schemas or catalogs first:

“`sql
SELECT * FROM training.sales.customers;
“`

This query explicitly references the `customers` table in the `sales` schema of the `training` catalog, providing clarity and precision in your SQL statements.

—

## Summary

In this lesson, you've learned how to use the three-level namespace in Unity Catalog: `Catalog.Schema.Object`.

– You used the `training` catalog.
– You optionally used the `sales` schema.
– You queried the `customers` table using both the schema-qualified and fully qualified namespace.

This structure helps you organize your data assets, improve security, and ensure clarity in your data workflows.