找到每个学生的类别数量

Question

我在MySQL数据库中有以下表格：

FirstName  LastName  ClubName
  ALAN     STURGES    Club1
ALESIA    BLACKBURN   Club2
ALESIA    BLACKBURN, 'Club 3'

我想知道每个学生所在的俱乐部数量。然后我想巩固报告，并根据他们所在俱乐部的数量显示学生人数。 例如：

students     Number of Clubs
  20                1
  40                2

Answer 1

GROUP BY和COUNT()条款将是您的英雄。

/*Knowing the number of clubs per student*/
SELECT COUNT(id) FROM your_tbl GROUP BY col_student_id;

和

/*Knowing the number of students per club*/
SELECT COUNT(id) FROM your_tbl GROUP BY col_club_id;

修改上述查询以满足您的需求结果。有关它的更多信息，请在此处阅读https://dev.mysql.com/doc/refman/5.5/en/group-by-handling.html

Answer 2

我猜

SELECT CONCAT(FirstName, ' ', LastName) as FULLNAME, COUNT(*) 
FROM TABLENAME 
GROUP BY FULLNAME;