mysql - mysql AND 在查询中使用了两次不起作用

Question

以下查询

SELECT * FROM workshops 
WHERE workshop_zipcode LIKE '75___' 
  OR workshop_zipcode LIKE '77___' 
  AND workshop_category = 14 
  AND active = 1 
  AND workshop_date >= NOW() 
ORDER BY workshop_date ASC

不产生任何错误，并且实际工作，但有一个小问题：这部分

AND workshop_date >= NOW()

不过滤任何东西，尝试用等号替换比较符号，并检索相同的列表。

前两个 AND 效果很好，但第三个不行。

Answer 1

你需要用括号括起来你的OR条件像这样：

SELECT * FROM workshops 
WHERE (workshop_zipcode LIKE '75___' 
OR workshop_zipcode LIKE '77___')
AND workshop_category = 14 
AND active = 1 
AND workshop_date >= NOW() 
ORDER BY workshop_date ASC

没有括号，你本质上是这样称呼的：

SELECT * FROM workshops 
WHERE workshop_zipcode LIKE '75___' 
OR (workshop_zipcode LIKE '77___'
AND workshop_category = 14 
AND active = 1 
AND workshop_date >= NOW())
ORDER BY workshop_date ASC

这是因为AND是之前计算的OR。请参阅此参考

http://dev.mysql.com/doc/refman/5.0/en/operator-precedence.html

Answer 2

这可能是运算符优先级的问题。

SQL 将首先评估您的所有 AND 语句，然后是 OR 语句；如果你在它们周围加上括号，你可能会得到你期望的结果：

SELECT * FROM workshops 
WHERE (workshop_zipcode LIKE '75___' 
OR workshop_zipcode LIKE '77___')
AND workshop_category = 14 
AND active = 1 
AND workshop_date >= NOW() 
ORDER BY workshop_date ASC

这将检查车间邮政编码，然后检查您的其他标准。

Answer 3

试试这个：

SELECT * FROM workshops 
WHERE ( workshop_zipcode LIKE '75___' 
OR workshop_zipcode LIKE '77___' )
AND workshop_category = 14 
AND active = 1 
AND workshop_date >= NOW() 
ORDER BY workshop_date ASC