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，实际上有效，但有一点问题：这部分

AND workshop_date >= NOW()

不要过滤任何内容，请用相等的符号替换比较符号，并检索相同的列表。

两个第一个AND效果很好，但第三个没有。

Answer 1

您需要为OR条件加上括号，如下所示：

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，你实质上就是这样称呼：

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是在OR之前计算的。参见此参考资料

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

Answer 2

这可能是运营商优先级的问题。

SQL将首先评估所有AND语句，然后评估OR语句;如果你在它们周围放置括号，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

这将检查研讨会的zipcodes，然后检查其余的标准。

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

mysql AND在查询中使用两次不起作用

3 个答案: