Connecting to SQL Databases

In this lesson, explore connecting to sql databases through one small Go program, and connect its output to the language rules behind it.

Call sql.Open(driverName, dsn) to obtain a reusable *sql.DB handle; it represents a connection pool, not necessarily one active connection. Use PingContext to check whether the configured database can be reached.

database/sql does not ship a database driver. The primary runnable example demonstrates this dependency explicitly, while the additional snippet shows how real connection code is structured.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

Real SQL connection pattern

Install and import a compatible database driver first. This snippet assumes driverName is registered and dsn is configured.

db, err := sql.Open(driverName, dsn)
if err != nil { return err }
defer db.Close()
ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
if err := db.PingContext(ctx); err != nil { return err }

Use an actual module and driver; this instructional fragment is not a standalone program. Reference: Open a database handle.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import (
	"database/sql"
	"fmt"
)

func main() {
	_, err := sql.Open("unregistered-demo-driver", "dsn")
	fmt.Println("Requires driver:", err != nil)
}

Output

Requires driver: true

The driver name has not been registered, so sql.Open returns an error; the program prints Requires driver: true. No database connection is attempted.

• sql.Open may return a handle without opening a network connection; use PingContext when testing connectivity.
• Never hard-code production passwords into source files.

With a locally installed driver, open a handle, defer Close, and call PingContext with a timeout.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Connecting to SQL Databases in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.