What does an underscore in front of an import statement mean?

In this code from go-sqlite3:

import (
        "database/sql"
        "fmt"
        _ "github.com/mattn/go-sqlite3"
        "log"
        "os"
)

what does the underscore in the import statement mean?

It's for importing a package solely for its side-effects.

From the Go Specification:

To import a package solely for its side-effects (initialization), use the blank identifier as explicit package name:
import _ "lib/math"


In sqlite3

In the case of go-sqlite3, the underscore import is used for the side-effect of registering the sqlite3 driver as a database driver in the init() function, without importing any other functions:

sql.Register("sqlite3", &SQLiteDriver{})

Once it's registered in this way, sqlite3 can be used with the standard library's sql interface in your code like in the example:

db, err := sql.Open("sqlite3", "./foo.db")

Stack Overflow Q#21220077, score: 337