Question

我有这张桌子

name   | prof      |grade
------------------------
yossi   math     100
tami    math     70
yossi   phisic   100
tami    phisic   100
oren    math     100
oren    phisic   80
dor     history  70

查询应该返回数学和phisic等级为100的学生的姓名正确的解决方案是yossi 我使用了以下

SELECT name FROM [dbo].[Class_grade]
where prof in ('math', 'phisic') and grade = 100

但是为什么会返回更多的名字？什么是正确的查询？感谢

Answer 1

select name
from Class_Grade
where grade = 100 and
      prof in ('math', 'phisic')
group by name
having count(distinct prof) = 2

按name分组，并使用having过滤掉行。确保计算prof的不同出现次数。在这种情况下它是2，因为你的in子句中有2个值。

Answer 2

之前我错误引用了 Question

您可以使用 Group by caluse

SELECT name FROM [Class_grade]
where prof in ('math', 'phisic') and grade = 100
group by (name)
having count(1)=2

<强> SQL FIDDLE

Answer 3

分组，并使suure得到两行

SELECT name 
FROM Class_grade
WHERE prof in ('math', 'phisic') and grade = 100
GROUP BY name
HAVING count(*) = 2

http://www.sqlfiddle.com/#!3/9308c/6

修改如果同一个学生在一个科目中可以有超过100％的成绩，你可以获得不同的成绩

SELECT name FROM ( SELECT DISTINCT name, prof, grade FROM Class_grade WHERE prof in ('math', 'phisic') and grade = 100 ) class_grade GROUP BY name HAVING count(*) = 2

http://www.sqlfiddle.com/#!3/79fd0/11

Answer 4

试试这个

SELECT name FROM Class_grade
WHERE prof IN ('math', 'phisic') AND grade=100
GROUP BY name
HAVING COUNT(name) > 1

Answer 5

OP没有说明一些细节：

桌子上的主键是什么（即同一个学生可以为同一个科目存在多条线路）
当有多名学生符合标准时，预期结果是什么。

如果我们假设一个学生可以在同一个科目中有多个成绩，那么HAVING COUNT(*)个条款中的许多其他答案都是错误的。 Mikael Eriksson's answer满足了这个假设，并且它可能比我的下面的解决方案更高效（尽管功能也有所不同）：

SELECT DISTINCT name FROM [dbo].[Class_grade] cg1
WHERE EXISTS (
  SELECT 1 FROM [dbo].[Class_grade] cg2
  WHERE cg2.name = cg1.name
  AND cg2.prof = 'math'
  AND cg2.grade = 100)
AND EXISTS (
  SELECT 1 FROM [dbo].[Class_grade] cg2
  WHERE cg2.name = cg1.name
  AND cg2.prof = 'phisic'
  AND cg2.grade = 100)
AND NOT EXISTS (
  SELECT 1 FROM [dbo].[Class_grade] cg2
  WHERE cg2.name = cg1.name
  AND cg2.prof in ('math','phisic')
  AND cg2.grade < 100)

上述代码的不同之处在于，它只会选择只有grade = 100 math和phisic科目的学生，即使他们每个科目的成绩可能超过一个。 See here

Answer 6

            select Class_grade.name
            from Class_grade
            inner join Class_grade Class_grade2
            on Class_grade.Name = Class_grade2.name
            where Class_grade.Prof = 'math' and Class_grade.grade = 100
            and Class_grade2.prof = 'phisic' and Class_grade2.grade = 100
            group by Class_grade.Name

尽量不要使用distinct，这是一个糟糕的编码

Answer 7

试试这个：

SELECT DISTINCT name  FROM [dbo].[Class_grade] where prof in ('math', 'phisic') and grade = 100

这也可行：

SELECT DISTINCT name FROM [dbo].[Class_grade] where (prof = 'math' and grade = 100) OR (prof = 'phisics' and grade = 100)

如何查询varchar和int

7 个答案: