mysql - 当 mysql 查询中缺少数据时，我想显示关系数据

Question

我想显示关系数据，当 mysql 查询中缺少数据时，我有以下查询

SELECT u.user_email, um1.value AS school, um.value AS postcode
FROM `wp_users` AS u, `wp_bp_xprofile_data` AS um, `wp_bp_xprofile_data` AS um1
WHERE u.ID = um.user_id
AND u.ID = um1.user_id
AND um.field_id =322
AND um1.field_id =69

这会显示一个电子邮件地址、学校名称和邮政编码。我想弄清楚的是如果学校或邮政编码不在数据库中，如何获取所有电子邮件，即即使数据丢失也显示值

干杯，有钱

Answer 1

SELECT u.user_email 
,       um1.value AS school
,       um.value AS postcode
FROM `wp_users` AS u
LEFT JOIN `wp_bp_xprofile_data` AS um
  ON u.ID = um.user_id
  AND um.field_id = 322
LEFT JOIN `wp_bp_xprofile_data` AS um1
  ON u.ID = um1.user_id
  AND um1.field_id = 69