Using the golang example below, how can I query (JOIN) multiple databases.
For example, I want to have the relation db1.username.id = db2.comments.username_id.
id := 123
var username string
err := db.QueryRow("SELECT username FROM users WHERE id=?", id).Scan(&username)
switch {
case err == sql.ErrNoRows:
log.Printf("No user with that ID.")
case err != nil:
log.Fatal(err)
default:
fmt.Printf("Username is %s\n", username)
}
As you are using MySQL, you can select fields across databases. See this related question for details. For example you should be able to do this:
err := db.QueryRow(`
SELECT
db1.users.username
FROM
db1.users
JOIN
db2.comments
ON db1.users.id = db2.comments.username_id
`).Scan(&username)
You can of course simply fetch all entries from db2.comments using a second database connection and use the values in a query to db1.users. This is, of course, not recommended as it is the job of the database server which it can, most likely, do better than you.
