Selecting User Data in WordPress Queries

Method using JOIN on the wp_user and wp_usermeta tables:

SELECT
    u1.id,
    u1.user_login,
    u1.user_password,
    u1.user_email,
    m1.meta_value AS firstname,
    m2.meta_value AS lastname,
    m3.meta_value AS country
FROM wp_users u1
JOIN wp_usermeta m1 ON (m1.user_id = u1.id AND m1.meta_key = 'first_name')
JOIN wp_usermeta m2 ON (m2.user_id = u1.id AND m2.meta_key = 'last_name')
JOIN wp_usermeta m3 ON (m3.user_id = u1.id AND m3.meta_key = 'country')
WHERE
    -- CONDITIONS ON the user you want to select --

Method without using JOIN (creating the VIEW is optional):

CREATE OR REPLACE VIEW users_with_meta_view AS
SELECT
    u.id,
    u.user_login AS login,
    u.user_pass AS password,
    u.user_email AS email,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'first_name' limit 1) as first_name,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'last_name' limit 1) as last_name,
    (select meta_value from wp_usermeta where user_id = u.id and meta_key = 'country' limit 1) as country
FROM wp_users u