根據條件和用戶輸入執行選擇語句 MySQL

Question

我試圖允許基於發送到IF條件的特定字符串執行特定的SELECT語句。 例如，如果用戶從下拉列表中選擇支持，則將變量鍵發送到 sql 語句，並執行相應的SELECT語句。

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 ，除非您將代碼放在編程塊中。 您的問題有點難以理解，因為文本提到了一個查詢，但代碼為兩個似乎相同。

您可以將條件邏輯移動到查詢中最外層的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)

我不確定這是你真正想要的。 我懷疑你想要：

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，這只是對在您描述的情況下有用的內容的知情推測。

筆記：

• 表別名使查詢更容易編寫和閱讀（就像適當的縮進一樣）。
• 不應使用單引號引入數字常量。 我猜 ids 真的是數字。 如果它們是字符串，那么單引號是合適的。