如何计算MySQL中不同项目的项目数？

Question

Imagine a have a table with a column named status:

status
------
A
A
A
B
C
C
D
D
D

How can I count how many rows have A, how many rows have B etc? this kind of output:

A  |B  |C  |D  |E  
------------------
3  |1  |2  |3  |0

As for E = O , this will always be A,B,C,D and E Output should be one row (thus 1 query).

When doing a distinct count (most returning answer on my searches, it does return how many different elements there are, 4 in this case...)

Answer 1

You simply need to group your table, applying a suitable aggregate function:

SELECT   status, COUNT(*)
FROM     my_table
GROUP BY status

See it on sqlfiddle .

If a status is missing, you can treat it as 0 from within your application code.

Answer 2

Putting the results into one row is a bit more clumsy that group by:

Select
    sum(status = 'A') 'A',
    sum(status = 'B') 'B',
    sum(status = 'C') 'C',
    sum(status = 'D') 'D',
    sum(status = 'E') 'E'
From 
    my_table

Some databases support pivot which makes this a bit better. MySQL isn't one of them.

Example SQLFiddle