Question

我有一些代码可以从mysql中获取一组结果，请参阅下面的内容，

SELECT string, COUNT(string) as myCount 
FROM ip_stats WHERE string != '' OR string IS NOT NULL 
GROUP BY string 
ORDER BY myCount DESC 
LIMIT 10

现在这段代码完美无缺，但是当我在下面添加另一个where子句时，它会返回相同的结果，并且似乎完全无视where where claus的member =部分？

SELECT string, COUNT(string) as myCount 
FROM ip_stats WHERE member_id = '000826' string != '' OR string IS NOT NULL 
GROUP BY string 
ORDER BY myCount DESC 
LIMIT 10

任何想法或建议表示赞赏。

Answer 1

你的where子句有一些错误：

WHERE member_id = '000826' string != '' OR string IS NOT NULL

应该是

WHERE member_id = '000826' AND (string != '' OR string IS NOT NULL)

Answer 2

AND-part has priority over the OR-part。放括号来解决这个问题：

SELECT string, COUNT(string) as myCount 
FROM ip_stats 
WHERE member_id = '000826' 
AND (string != '' OR string IS NOT NULL)
GROUP BY string 
ORDER BY myCount DESC 
LIMIT 10

你写的东西实际上给了这个，这不是你想要的：

WHERE (member_id = '000826' AND string != '')
OR string IS NOT NULL

Answer 3

这没有意义，所以我认为这可能不是你想要的：

WHERE string != '' OR string IS NOT NULL

string IS NOT NULL将返回所有非空值（包括''）。

我猜你要排除空字符串和空字符串值，在这种情况下，这可能是你想要的查询：

SELECT string, COUNT(string) as myCount 
FROM ip_stats 
WHERE member_id = '000826' 
AND string IS NOT NULL 
AND string != '' 
GROUP BY string 
ORDER BY myCount DESC 
LIMIT 10

Mysql组查询出错

3 个答案: