MySQL 每个派生表都必须有自己的别名

Question

您好，我需要通过连接两个查询来生成一个 sql 查询

第一个查询:获取所有学生数据

SELECT * FROM students where class = 1 and section = 'A'

第二个查询:获取每次出席的次数

SELECT  roll_no,full_name, 

SUM(hasAttended= 'P') AS DaysPresent, 

SUM(hasAttended= 'A') AS DaysAbsent, 

COUNT(*) AS totalClasses

FROM     attendance

GROUP BY roll_no

现在我需要连接两个表并生成一个结果表

我正在尝试以下查询但出现错误:

1248 - Every derived table must have its own alias

我的查询如下:

SELECT * FROM students as st

INNER JOIN 

(SELECT  att.roll_no,att.full_name, 

SUM(att.hasAttended= 'P') AS DaysPresent, 

SUM(att.hasAttended= 'A') AS DaysAbsent, 

COUNT(*) AS totalClasses

FROM     attendance as att

GROUP BY att.roll_no)

ON st.roll_no = att.roll_no

ORDER BY  st.roll_no

谁能解决上面的错误

Answer 1

MySQL 要求所有派生表和子查询都有一个别名。您在子查询的右括号末尾缺少别名:

SELECT * 
FROM students as st
INNER JOIN 
(
  SELECT  att.roll_no,att.full_name, 
    SUM(att.hasAttended= 'P') AS DaysPresent, 
    SUM(att.hasAttended= 'A') AS DaysAbsent, 
    COUNT(*) AS totalClasses
  FROM     attendance as att
  GROUP BY att.roll_no
) att  ---------------------------< this is missing
  ON st.roll_no = att.roll_no
WHERE st.class = 1 
ORDER BY  st.roll_no