Question

我无法添加条件，只显示出勤率低于81的人。

SELECT Absence.StudentID AS StudentNumber,
   Student.NAME AS "Student Name",
   Subject.NAME AS "Subject Name",
   CONVERT(VARCHAR, 100 - (100 * count(*) / 10)) AS 'Attendance(%)'
FROM Absence,
   Subject,
   Student,
   (
      SELECT COUNT(*) AS tot
      FROM Absence
      ) x
WHERE Subject.SubjectCode = Absence.SubjectCode
   AND Student.StudentNumber = Absence.StudentID
GROUP BY Absence.StudentID,
   Subject.NAME,
   Student.NAME;

以上是完全显示我想要的代码，但我不能仅添加条件。我的出勤率（％）已经是正确的吗？所以使用CAST或CONVERT也不起作用。它说转换有问题。

Answer 1

这是数学中的隐式数据类型转换

select 100/50 as intMath , 100.00/50.00 as nbrMath

Answer 2

当试图获得百分比时，它会乘以100并且是DECIMAL，这似乎不是代码的工作方式：

SELECT (CAST(9 AS DECIMAL(5,2))/CAST(10 AS DECIMAL(5,2)))*CAST(100 AS DECIMAL(5,2))
-- Returns 90.00

SELECT (CAST(9 AS INT)/CAST(10 AS INT))*CAST(100 AS INT)
-- Returns 0

使用您的OP示例：

SELECT CAST(100 AS DECIMAL(5,2)) - ((CAST(100 AS DECIMAL(5,2)) * CAST(8 AS DECIMAL(5,2))) / CAST(10 AS DECIMAL(5,2)))
-- Returns 20.00

-- Formatted with a percent:
SELECT SUBSTRING(CAST(CAST(100 AS DECIMAL(5,2)) - ((CAST(100 AS DECIMAL(5,2)) * CAST(8 AS DECIMAL(5,2))) / CAST(10 AS DECIMAL(5,2))) AS VARCHAR(25)),1,5) + '%'

注意：这适用于SQL Server 。 90％是.9，当它是CAST AS INT时被视为0。

SQL代码无法以百分比格式显示出席情况

2 个答案: