SQL join 예제

wp_users:
id | login | password | email
-----------------------------
1 | bsmith| abc123 | b@foo.com
2 | jjones| def456 | k@bah.com

wp_usermeta:
id | user_id | meta_key | meta_value
------------------------------------
1 | 1 | firstname| bob
2 | 1 | lastname | smith
3 | 1 | country | denmark
4 | 2 | firstname| jan
5 | 2 | lastname | jones
6 | 2 | country | germany

MYSQL VIEW:
id | login | password | email | firstname | lastname | country
-----------------------------------------------------------------
1 | bsmith| abc123 | b@foo.com| bob | smith | denmark
2 | jjones| def456 | k@bah.com| jan | jones | germany


SQL >
SELECT
u1.ID,
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');