To access databases in Go, you use a sql.DB. You use this type to create statements and transactions, execute queries, and fetch results.

The first thing you should know is that a sql.DB isn’t a database connection. It also doesn’t map to any particular database software’s notion of a “database” or “schema.” It’s an abstraction of the interface and existence of a database, which might be as varied as a local file, accessed through a network connection, or in-memory and in-process.

sql.DB performs some important tasks for you behind the scenes:

• It opens and closes connections to the actual underlying database, via the driver.
• It manages a pool of connections as needed, which may be a variety of things as mentioned.

The sql.DB abstraction is designed to keep you from worrying about how to manage concurrent access to the underlying datastore. A connection is marked in-use when you use it to perform a task, and then returned to the available pool when it’s not in use anymore. One consequence of this is that if you fail to release connections back to the pool, you can cause sql.DB to open a lot of connections, potentially running out of resources (too many connections, too many open file handles, lack of available network ports, etc). We’ll discuss more about this later.

After creating a sql.DB, you can use it to query the database that it represents, as well as creating statements and transactions.

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