Go 언어를 사용한 MySQL 데이터베이스의 데이터 작업 사전 검증

import (
    "database/sql"
    "fmt"

    _ "github.com/go-sql-driver/mysql"
)

func main() {
    // Open up our database connection.
    db, err := sql.Open("mysql", "user:password@tcp(127.0.0.1:3306)/database")
    if err != nil {
        log.Fatal(err)
    }

    // Verify the connection with the Ping() method.
    if err := db.Ping(); err != nil {
        log.Fatal(err)
    }

    // Do something with the newly opened connection here.
    // ...
}

func insertData(db *sql.DB, username string, password string) error {
    // Ensure username and password are not empty.
    if len(username) == 0 || len(password) == 0 {
        return errors.New("username and password are required")
    }

    // In the real world, ensure the username doesn't exist before creating a new user.
    if userExists(db, username) {
        return errors.New("user already exists")
    }

    // Perform the insert operation.
    _, err := db.Exec("INSERT INTO users (username, password) VALUES (?, ?)", username, password)
    if err != nil {
        return err
    }

    return nil
}

func userExists(db *sql.DB, username string) bool {
    // Prepare the SQL statement.
    stmt, err := db.Prepare("SELECT count(*) FROM users WHERE username = ?")
    if err != nil {
        return false
    }
    defer stmt.Close()

    // Execute the SQL statement.
    var count int
    err = stmt.QueryRow(username).Scan(&count)
    if err != nil {
        return false
    }

    return count > 0
}

func getUsers(db *sql.DB, username string) ([]User, error) {
    // Ensure the username parameter is not empty.
    if len(username) == 0 {
        return nil, errors.New("username is required")
    }

    // Prepare the SQL statement.
    stmt, err := db.Prepare("SELECT * FROM users WHERE username = ?")
    if err != nil {
        return nil, err
    }
    defer stmt.Close()

    // Execute the SQL statement with the given username parameter.
    rows, err := stmt.Query(username)
    if err != nil {
        return nil, err
    }
    defer rows.Close()

    // Collect the query results into a slice of User objects.
    var users []User
    for rows.Next() {
        var u User
        err := rows.Scan(&u.Username, &u.Password)
        if err != nil {
            return nil, err
        }
        users = append(users, u)
    }

    return users, nil
}