Question

del = 0 - 未删除，del = 1 - 发件人和收件人已删除邮件，del2 - 发件人已删除邮件，del = 3 - 收件人已删除邮件。我的代码是：

SELECT
    *
FROM
    messages
WHERE
    (`from` = :owner AND `to` = :partner) OR (`from` = :partner AND `to` = :owner) AND IF(`from` = :owner,`del`=3 OR `del`=0,`del`=2 OR `del`=0)
ORDER BY
    id DESC

但它不起作用。请帮助。

Answer 1

很可能你遇到了IF()函数返回字符串或数值的问题。但是你似乎期望它返回一个布尔值。（SQL没有布尔数据类型。）

所以你必须使用IF()的替代方法：

SELECT
    *
FROM
    messages
WHERE
    (`from` = :owner AND `to` = :partner)
 OR (`from` = :partner AND `to` = :owner)
    AND (`from` = :owner AND `del` IN (0, 3)
        OR `from` <> :owner AND `del` IN (0, 2))
ORDER BY
    id DESC

如果from和:owner不能为NULL，则应该相同。否则from <> :owner需要一些NULL处理。

BTW。：你真的只想为OR表达式的第二部分测试del标志吗？因为这就是SQL如何评估它（AND之前的OR）。

<强>更新

从您的评论中，我必须假设评估顺序确实是错误的。因此，我正在改变它：

SELECT
    *
FROM
    messages
WHERE
  (
    (`from` = :owner AND `to` = :partner)
    OR (`from` = :partner AND `to` = :owner)
  )
  AND (`from` = :owner AND `del` IN (0, 3)
      OR `from` <> :owner AND `del` IN (0, 2))
ORDER BY
    id DESC

IF在WHERE子句中

1 个答案: