MySQL-计算基于另一列的一列中的不同值

Question

i have the table resources which contains all data, i want to get the result as given in last table.. Please help me

Dept Grade
A    E3  
B    M2  
D    E3  
C    M1  
A    E3  
D    E4  
A    E3    

i used the below code but i am not able to get the actual solution

SELECT DISTINCT Department,COUNT(DISTINCT GRADE) as Grades FROM reslookup GROUP BY Department;

Executed Result for the about query,

Dept Grade
A    3
B    1
C    1
D    2

But, i want to get the result like given below

Dept E3  E4  M1  M2
A    5   0   2   1
B    4   2   3   0
C    8   9   2   1
D    5   0   2   6

Answer 1

What you are trying to do is pivot rows of the counts into different columns, and this can be done as following:

SELECT Dept,
  SUM(CASE WHEN Grade = 'E3' THEN 1 ELSE 0 END) AS E3, 
  SUM(CASE WHEN Grade = 'E4' THEN 1 ELSE 0 END) AS E4,
  SUM(CASE WHEN Grade = 'M1' THEN 1 ELSE 0 END) AS M1,
  SUM(CASE WHEN Grade = 'M2' THEN 1 ELSE 0 END) AS M2
FROM reslookup 
GROUP BY Dept;

demo

Answer 2

You can also use the below code which gives the same solution

SELECT Dept,
      SUM(Grade = 'E3') AS E3, 
      SUM(Grade = 'E4') AS E4,
      SUM(Grade = 'M1') AS M1,
      SUM(Grade = 'M2') AS M2
    FROM reslookup 
    GROUP BY Dept;