MySQL中的减号运算符？

Question

我有一些表格可以用来接收电子邮件。而且我不想收到表tbl_unsubscribe 中的电子邮件。我写了这样的查询：

SELECT cand_email FROM tbl_cand_data
UNION
SELECT emp_email FROM tbl_emp_data
UNION
SELECT email FROM tbl_uptade_list
UNION
SELECT feed_email FROM tbl_feedback
UNION
SELECT admin_email FROM tbl_admin_emails    

但我收到语法错误。 MINUS 运算符对 MySQL 无效吗？

Answer 1

这里可以使用NOT IN() 子查询，因为MySQL 不支持MINUS。

SELECT 
  cand_email
FROM tbl_cand_data 
WHERE can_email NOT IN (SELECT un_email FROM tbl_unsubscribe)

也可以使用LEFT JOIN 来完成，在un_email 列中查找NULL：

SELECT cand_email 
FROM
   tbl_cand_data
   LEFT JOIN tbl_unsubscribe ON tbl_cand_data.can_email = tbl_unsubscribe.un_email
WHERE tbl_unsubscribe.un_email IS NULL

要将它们从一堆UNION 操作中排除，请将UNION 组包装在() 中作为子查询：

SELECT email FROM (
  SELECT cand_email AS email FROM tbl_cand_data
  UNION
  SELECT emp_email AS email FROM tbl_emp_data
  UNION
  SELECT email FROM AS email tbl_uptade_list
  UNION
  SELECT feed_email AS email FROM tbl_feedback
  UNION
  SELECT admin_email AS email FROM tbl_admin_emails
) email_list
WHERE email NOT IN (SELECT un_email FROM tbl_unsubscribe)

Answer 2

不幸的是，MINUS 和 INTERSECT 不受 MySQL 支持，但您可以使用 JOIN 为MINUS 获得相同的结果，UNION 为INTERSECT。

SELECT cand_email FROM tbl_cand_data
LEFT JOIN tbl_unsubscribe ON (cand_email = un_email)
WHERE un_email IS NULL