The database/sql package
- Go course
- Advanced
- Lesson 25/68
- 4 min
Learn the basics of the database/sql package.
The database/sql package
database/sql offers a common interface for all SQL databases; a driver does the actual talking. The driver is imported with the blank identifier for its side effect and registers itself:
import (
"database/sql"
_ "github.com/go-sql-driver/mysql"
)The rest of the code is database-independent: moving from MySQL to PostgreSQL usually changes only the driver and the connection string.
sql.DB is a pool
*sql.DB is not a single connection but a connection pool. It is created once at startup and shared by all goroutines; opening and closing it per request is wrong. You tune the pool with SetMaxOpenConns, SetMaxIdleConns and SetConnMaxLifetime.
Practice Registered drivers
sql.Drivers() returns the names of registered drivers. Without importing any driver, print len(sql.Drivers()).
Starter code
package main
import (
"database/sql"
"fmt"
)
func main() {
// buraya yaz
}Sample solution
package main
import (
"database/sql"
"fmt"
)
func main() {
fmt.Println(len(sql.Drivers()))
}Expected output
0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Why is a driver package imported with <code>_</code>?
- For testing
- So that it only registers itself in init Correct answer
- So it compiles faster
- To keep it secret
Explanation: The driver's init function calls sql.Register; since you don't use the package name in code, the blank identifier is needed.
2 Register the driver
import (
"database/sql"
____ "github.com/lib/pq"
)import (
"database/sql"
_ "github.com/lib/pq"
)Explanation: The blank identifier imports the package only for its init side effect.
3 database/sql parts
| Term | Meaning |
|---|---|
database/sql |
Common interface |
Driver |
Talks to the database |
*sql.DB |
Connection pool |
SetMaxOpenConns |
Pool limit |