php MySQL中的减号运算符？
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MINUS operator in MySQL?
提问by AssamGuy
I have some tables where I am getting the emails. And I don't want to get the emails in table tbl_unsubscribe. I wrote the query like :
我有一些表格可以用来接收电子邮件。而且我不想收到 table 中的电子邮件tbl_unsubscribe。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
But I am getting a syntax error. Is the MINUSoperator not valid for MySQL ?
但我收到语法错误。是MINUS运营商无效为MySQL？
回答by Michael Berkowski
A NOT IN()subquery can be used here, since MySQL doesn't support MINUS.
一个NOT IN()子查询可以在这里使用，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)
It can also be done with a LEFT JOIN, looking for NULLs in the un_emailcolumn:
也可以使用 a 来完成，LEFT JOIN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
To exclude them from a bunch of UNIONoperations, wrap the UNIONgroup in ()as a subquery:
要将它们从一系列UNION操作中排除，请将UNION组包装()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)
回答by Maxim Krizhanovsky
Unfortunately MINUSand INTERSECTare not supported by MySQL, but you can get the same result using JOINfor MINUS, UNIONfor INTERSECT.
遗憾的是MINUS并INTERSECT用的MySQL不支持，但你可以使用得到相同的结果JOIN为MINUS，UNION对INTERSECT。
SELECT cand_email FROM tbl_cand_data
LEFT JOIN tbl_unsubscribe ON (cand_email = un_email)
WHERE un_email IS NULL
