SQL USE: select database

Let's go through the USE statement in SQL.

The USE statement is a simple command that is used to select a specific database to work with. This command is useful when you have multiple databases in your SQL schema.

Here's the basic syntax:

USE database_name;

Let's say you have a database called Employees and you want to work with it. To select this database, you would use the following command:

USE Employees;

Once this statement is executed, the Employees database will be used for any subsequent SQL queries until you either close the connection or select a different database.

It's important to note that the USE statement is specific to some database systems, such as MySQL and Microsoft SQL Server. In other database systems like Oracle or PostgreSQL, you typically connect directly to a database, and the USE statement does not exist.

Also, you should have the necessary privileges to access the database you want to use. If you don't have the necessary privileges, you may encounter an error when trying to select the database.

That's pretty much it! The USE statement is a simple but useful command when you're working with multiple databases.

Selecting a Database in SQL with USE:
- Description: USE is used to switch the current database context in SQL.
- Code Example:
```
USE your_database;
```
Changing the Active Database in SQL:
- Code Example:
```
USE your_database;
```
How to Switch Databases in SQL:
- Code Example:
```
USE another_database;
```
USE Database in [Your Database System]:
- Code Example (MySQL):
```
USE your_database;
```
- Code Example (SQL Server):
```
USE your_database;
```
- Code Example (PostgreSQL):
```
\c your_database;
```
- Code Example (Oracle):
```
ALTER SESSION SET CURRENT_SCHEMA = your_database;
```

Managing Multiple Databases with SQL USE:

Code Example:

USE database1;
-- Execute queries in database1

USE database2;
-- Execute queries in database2

SQL USE vs Specifying Database in Queries:
- Difference: USE sets the default database for subsequent queries, while specifying the database in queries affects only that specific query.
- Example:
```
USE database1;
SELECT * FROM table1; -- Table1 in database1

SELECT * FROM database2.table2; -- Table2 in database2 without changing the default database
```
Checking the Current Database in SQL:
- Code Example:
```
SELECT DB_NAME() AS CurrentDatabase;
```

SQL USE in Stored Procedures:

Code Example:

CREATE PROCEDURE your_procedure
AS
BEGIN
    USE your_database;
    -- Procedure logic
END;

Switching Databases in SQL Scripts:

Code Example:

USE database1;
-- Script logic for database1

USE database2;
-- Script logic for database2

Undoing a SQL USE Statement:
- Description: There is no direct command to undo a USE statement. Simply issue another USE statement for the desired database.
- Code Example:
```
USE original_database; -- Switch back to the original database
```