根据条件和用户输入执行选择语句 MySQL

Question

我试图允许基于发送到IF条件的特定字符串执行特定的SELECT语句。 例如，如果用户从下拉列表中选择支持，则将变量键发送到 sql 语句，并执行相应的SELECT语句。

DECLARE @ strg
SET @strg = 'input string'
IF(SELECT * FROM tickets WHERE ticket_section = @strg)
BEGIN
SELECT
usr_users.uname AS `user`,
support_chat_user.message AS user_message,
support_chat_user.created AS user_chat_date,
support_ticket.`subject` AS ticket_subject,
support_ticket.`status` AS ticket_state,
support_ticket.created AS ticket_date,
support_ticket.modified AS updated_date,
tickets.state
FROM
tickets
INNER JOIN support_chat_user ON support_chat_user.tickets_id = tickets.tick_id
INNER JOIN support_ticket ON support_ticket.tickets_id = tickets.tick_id
INNER JOIN usr_users ON support_chat_user.reporter_id = usr_users.uid
WHERE
tickets.tick_id = '9' AND
usr_users.uid = '1'
END

IF EXISTS(SELECT * FROM tickets WHERE ticket_section = @strg)

BEGIN
SELECT
usr_users.uname AS `user`,
support_chat_user.message AS user_message,
support_chat_user.created AS user_chat_date,
support_ticket.`subject` AS ticket_subject,
tickets.state
FROM
tickets
INNER JOIN support_chat_user ON support_chat_user.tickets_id = tickets.tick_id
INNER JOIN support_ticket ON support_ticket.tickets_id = tickets.tick_id
INNER JOIN usr_users ON support_chat_user.reporter_id = usr_users.uid
WHERE
tickets.tick_id = '9' AND
usr_users.uid = '1'

END

Answer 1

MySQL 不支持IF ，除非您将代码放在编程块中。 您的问题有点难以理解，因为文本提到了一个查询，但代码为两个似乎相同。

您可以将条件逻辑移动到查询中最外层的WHERE子句：

SELECT u.uname AS `user`, scu.message AS user_message, scu.created AS user_chat_date,
       st.`subject` AS ticket_subject, st.`status` AS ticket_state, st.created AS ticket_date, st.modified AS updated_date,
       t.state
FROM tickets t JOIN
     support_chat_user scu
     ON scu.tickets_id = t.tick_id JOIN
     support_ticket st
     ON st.tickets_id = t.tick_id JOIN
     usr_users u
     ON scu.reporter_id = u.uid
WHERE t.tick_id = 9 AND  -- presumably this is not numeric
      u.uid = 1 AND      -- presumably this is not numeric
      EXISTS (SELECT 1 FROM tickets t2 WHERE t2.ticket_section = @strg)

我不确定这是你真正想要的。 我怀疑你想要：

WHERE t.tick_id = 9 AND  -- presumably this is not numeric
      u.uid = 1 AND      -- presumably this is not numeric
      (t.ticket_section = @strg OR @strg IS NULL)

但是，这只是对在您描述的情况下有用的内容的知情推测。

笔记：

• 表别名使查询更容易编写和阅读（就像适当的缩进一样）。
• 不应使用单引号引入数字常量。 我猜 ids 真的是数字。 如果它们是字符串，那么单引号是合适的。