Question

我为学生提供了这个样本多对多表格＆amp;大学的科目

student | subject
-----------------
James   | English
James   | Physics
Paul    | Mathematics
Paul    | English
Paul    | English
Paul    | French
Jake    | French
Jake    | Mathematics
Paul    | English

我需要知道SQL查询，以获取每个学生的主题数量，如

student | # of subjects
------------------------
James   |   2
Paul    |   3
Jake    |   2

Answer 1

您需要的只是GROUP BY student和COUNT(DISTINCT)：

SELECT student, COUNT(DISTINCT subject) AS "# of subjects" 
FROM students_subjects
GROUP BY student;

Answer 2

您需要分组

$(function(){
$(".dropdown").hover(            
        function() {
            $('.dropdown-menu', this).stop( true, true ).fadeIn("fast");
            $(this).toggleClass('open');
            $('b', this).toggleClass("caret caret-up");                
        },
        function() {
            $('.dropdown-menu', this).stop( true, true ).fadeOut("fast");
            $(this).toggleClass('open');
            $('b', this).toggleClass("caret caret-up");                
        });
});

Answer 3

SELECT student, count(*) 
FROM table
GROUP BY student

Answer 4

您需要按学生分组：

SELECT student, count(*) as NumberOfSubjects
FROM table_name
GROUP BY student

Answer 5

Select student , count(subject) from Table Group by student

SQL计数第二列 - 第一列的每个唯一行

5 个答案: