Question

我有一个非常大的数据库。我需要运行查询以通过电子邮件和load_date（日期/时间戳字段）进行搜索。我需要从3个不同的日期中抽出3个电子邮件用户。

所以我需要一个表来显示电子邮件（电子邮件字段）：

email1@host.com
nextemail@site.com
finalemail.yosite.com

表示日期（load_date字段）：

2014-08-01
2014-08-06
2014-08-09

如果我这样做：

SELECT email, load_date
  FROM table1
  WHERE email = 'email1@host.com' or email = 'nextemail@site.com' or email = 'finalemail.yosite.com

结果是正确的。

如果我跑：

SELECT email, load_date
  FROM table1
  WHERE load_date LIKE "2014-08-01%" or load_date LIKE "2014-08-06%" or load_date LIKE "2014-08-09%"

结果是正确的。

但如果我把它们结合起来：

SELECT email, load_date
  FROM table1
  WHERE email = 'email1@host.com' or email = 'nextemail@site.com' or email = 'finalemail.yosite.com'
  and
   load_date LIKE "2014-08-01%" or load_date LIKE "2014-08-6%" or load_date LIKE "2014-08-09%"

我得到了一切！？

我做错了什么？

Answer 1

AND函数具有比OR函数更高的优先级。您需要将OR包含在括号中。

SELECT email, load_date
FROM table1
WHERE (email = 'email1@host.com' or email = 'nextemail@site.com' or email = 'finalemail.yosite.com')
and (load_date LIKE "2014-08-01%" or load_date LIKE "2014-08-6%" or load_date LIKE "2014-08-09%")

Answer 2

您需要使用括号：

SELECT email, load_date
  FROM table1
  WHERE (email = 'email1@host.com' or email = 'nextemail@site.com' or email = 'finalemail.yosite.com'(
  and
   (load_date LIKE "2014-08-01%" or load_date LIKE "2014-08-6%" or load_date LIKE "2014-08-09%")

Answer 3

二元运算符从左到右进行评估，and优先于or。

示例：如果condX是布尔条件，则cond1 or cond2 and cond3 or cond4的评估如下：

cond1或cond2
[上述结果]和cond3
[上述结果]和cond4

如果你想＆＃34;改变＆＃34;您的条件的评估顺序，您必须将它们括在括号中。

在您的具体情况下，您必须在括号内括出email比较和load_date比较：

WHERE 
    (email = 'email1@host.com' or email = 'nextemail@site.com' or email = 'finalemail.yosite.com')
  and (load_date LIKE "2014-08-01%" or load_date LIKE "2014-08-6%" or load_date LIKE "2014-08-09%")

备选方案：使用in：

WHERE email in ('email1@host.com', 'nextemail@site.com', 'finalemail.yosite.com')
  AND date(load_date) in ("2014-08-01", "2014-08-6", "2014-08-09")
-- date(load_date) extracts the date part of the field

具有多个WHERE的MYSQL查询

3 个答案: