Question

我在sql的新手，我想知道为什么这个在我创建我的SQL查询到视图时出错

mysql查询：

SELECT staffid AS staff,   
(SELECT count( feedback )FROM msqueue WHERE staffid = staff AND feedback =1) AS a,
(SELECT count( feedback )FROM msqueue WHERE staffid = staff AND feedback =2) AS b,
(SELECT count( feedback )FROM msqueue WHERE staffid = staff AND feedback =3) AS c,
(SELECT count( feedback )FROM msqueue WHERE staffid = staff AND feedback =4) AS d
FROM msqueue
GROUP BY staffid

这个查询结果就像我想要的那样

|staff| a | b | c | d |     
|d1111| 0 | 1 | 1 | 0 |    
|d1234| 1 | 2 | 4 | 0 |

但是当我创建查询作为视图时结果是

|staff| a | b | c | d |     
|d1111| 1 | 3 | 5 | 0 |    
|d1234| 1 | 3 | 5 | 0 |

请帮助我解释这段代码发生的事情..非常感谢

Answer 1

尝试

SELECT staffid AS staff,   
(SELECT count(*) FROM msqueue n WHERE n.staffid = m.staffid AND feedback =1) AS a,
(SELECT count(*) FROM msqueue n WHERE n.staffid = m.staffid AND feedback =2) AS b,
(SELECT count(*) FROM msqueue n WHERE n.staffid = m.staffid AND feedback =3) AS c,
(SELECT count(*) FROM msqueue n WHERE n.staffid = m.staffid AND feedback =4) AS d
FROM msqueue m
GROUP BY staffid

在原始查询中，您使用主要选择列staffid的别名将其与子查询的staffid列配对。这不足以区分两列，因此您可以获得每行中所有内容的总和。通过在列名前面使用表别名m和n，我们现在可以清楚地解决这两个问题。列。

见这里：http://sqlfiddle.com/#!9/ab25a9/1

您甚至可以在子查询中省略表别名，例如

SELECT staffid AS staff,   
(SELECT count(*) FROM msqueue WHERE staffid = m.staffid AND feedback =1) AS a,
(SELECT count(*) FROM msqueue WHERE staffid = m.staffid AND feedback =2) AS b,
(SELECT count(*) FROM msqueue WHERE staffid = m.staffid AND feedback =3) AS c,
(SELECT count(*) FROM msqueue WHERE staffid = m.staffid AND feedback =4) AS d
FROM msqueue m
GROUP BY staffid

http://sqlfiddle.com/#!9/ab25a9/2

修改

毕竟这是＆＃34;聪明的＆＃34;从我这边我刚刚发现，你原来的陈述是有效的 - 至少是＃34;它自己的＃34; （http://sqlfiddle.com/#!9/ab25a9/4）。我还没有尝试过把它放在视图中。当事情开始出错时，也许就是这个问题。更安全的选择肯定是使用表别名。

是的，当你把它放在视图中时，ist 出错了！但是对于外部查询至少有一个表别名，一切正常：http://sqlfiddle.com/#!9/f5f1e/1

我首先使用 MySql 对其进行了测试，但语句相同，并且在 SQL-Server 中的工作方式相同，请参阅此处http://sqlfiddle.com/#!6/f5f1e/1

Answer 2

我无法访问mysql服务器来测试它，但只是在一般的SQL术语中，这可能是一个更简单的解决方案：

SELECT 
   staffid AS staff,   
   SUM(CASE WHEN feedback = 1 THEN 1 ELSE 0 END) AS a,
   SUM(CASE WHEN feedback = 2 THEN 1 ELSE 0 END) AS b,
   SUM(CASE WHEN feedback = 3 THEN 1 ELSE 0 END) AS c,
   SUM(CASE WHEN feedback = 4 THEN 1 ELSE 0 END) AS d
FROM 
   msqueue
GROUP BY 
   staffid

转换为视图时sql参数错误

2 个答案: