如何根据列值对行进行计数？

Question

Using PHP and MySQL, I have a table that holds check in data for customers: the month and year they checked in.

ID  Month   Year

1   01      2015
1   01      2015
4   01      2015
1   03      2015
4   03      2015
1   05      2015

I need a total count of rows per month and year. So in this example I should get a total of 3 for id 1 for the month of 01 and year 2015. I'm adding the total days a person checked in for each month of each year.

Having a problem getting started with the code. I assume I can do this with MySQL count or something.

Answer 1

you can using mysql function are "GROUP BY

select count(id) from table group by year

Answer 2

You can use MySQL COUNT() function with GROUP BY like:

  SELECT ID, Month, Year, COUNT(*)
    FROM checked_customer
    GROUP BY ID, Month, Year;