Question

SELECT * FROM mm_tfs 
WHERE product_slug LIKE '%football%' 
    AND schoolid = '8' AND category_id ='21'
LIMIT 4

返回4个值，就像我问的那样，但是下面的语句返回0 - 是否有关于使用我不熟悉的OR语句的规则？我的假设是它应该返回1中的所有值（如果不是限制，则返回更多值）。

SELECT * FROM mm_tfs 
WHERE (product_slug LIKE '%football%' 
   AND schoolid = '8' AND category_id ='21') 
OR (product_description LIKE '%football%' 
   AND schoolid = '8' AND category_id ='21') 
LIMIT 4

_{cyberkiwi注意 Q2的第一个OR部分与Q1上的WHERE子句完全相同}

product_description LIKE '%football%' AND schoolid = '8' AND category_id ='21

没有OR语句本身只要没有限制就会产生所需的结果。当OR语句与LIMIT一起使用时，返回0值。

SELECT * FROM mm_tfs 
WHERE product_description LIKE '%football%' 
    AND schoolid = '8' AND category_id ='21'
LIMIT 4

^ - 产生0结果

SELECT * FROM mm_tfs 
WHERE product_description LIKE '%football%' 
    AND schoolid = '8' AND category_id ='21'

^ - 产生结果

最奇怪的是，所有这些查询在我的PHPMYADMIN SQL查询窗口中产生了正确的效果，但在应用程序本身中却没有。

Answer 1

尝试将（）放在整个条件

( (...AND...) OR (...AND...) )

像这样：

  SELECT * FROM mm_tfs WHERE 
  (  (product_slug LIKE '%football%' AND schoolid = '8' AND category_id ='21') 
   OR (product_description LIKE '%football%' AND schoolid = '8' AND category_id   
   ='21')
  ) LIMIT 4

Answer 2

您正在重复一些不必要的条件。试试这个：

SELECT * FROM mm_tfs 
WHERE 
   (product_slug LIKE '%football%' 
 OR product_description LIKE '%football%')
   AND schoolid = '8' 
   AND category_id ='21'
LIMIT 4

<强>更新

我创建了下表：

create table mm_tfs2 (schoolid varchar(2), categoryid varchar(2), 
                      description varchar(20), slug varchar(20));

并且5次：

insert into mm_tfs2 values (8, 21, '', 'football');

最后查询：

select * from mm_tfs2 where 
(slug like '%football%' and schoolid = 8 and categoryid = 21) 
or (description like '%football%' and schoolid = 8 and categoryid = 21) 
limit 4;
+----------+------------+-------------+----------+
| schoolid | categoryid | description | slug     |
+----------+------------+-------------+----------+
| 8        | 21         |             | football |
| 8        | 21         |             | football |
| 8        | 21         |             | football |
| 8        | 21         |             | football |
+----------+------------+-------------+----------+
4 rows in set (0.00 sec)

所以我很遗憾地说我无法重现这个问题。

Answer 3

我认为你可以清理一下，你只能获得一所学校的行和一个类别ID，所以你没有理由要检查这两个时间：

SELECT *
FROM mm_tfs
WHERE schoolid = '8'
    AND category_id ='21'
    AND (product_slug LIKE '%football%'
         OR product_description LIKE '%football%')
LIMIT 4;

SQL LIMIT在没有LIMIT返回结果的情况下不返回任何结果

3 个答案: