Group data by Year and Month

Question

I have a table with 4 columns:

 1. customerID
 2. dateAdded
 3. productID
 4. quantity

The format of dateAdded is like this: 20180730 ( YearMonthDay ).

I want to group the rows in the table by year and month.

I tried the code below but it doesn't work. I still see rows with the same year and month repeated, but different day.

SELECT dateAdded
     , SUM(quantity) 
  FROM testTable 
 GROUP 
    BY DATE_FORMAT(dateAdded, '%Y%m')
     , dateAdded 
 ORDER 
    BY dateAdded DESC

Any idea how to fix this?

Thank you

Answer 1

Do not group by what you do not want the data to be grouped. Since you provide dateAdded as a parameter to be grouped with, it splits the data by dateAdded and you gain nothing out of year-month grouping. Remove the columns from select/groupby that you use for grouping like this:

SELECT DATE_FORMAT(dateAdded, '%Y%m')
     , SUM(quantity) 
FROM testTable 
GROUP BY 
     DATE_FORMAT(dateAdded, '%Y%m')

Answer 2

If you store dateAdded as 20180730, looks like it's a string, so it wont work with DATE_FORMAT function, you can use SUBSTRING instead

something like

SELECT dateAdded, SUM(quantity), SUBSTRING(dateAdded, 1, 6) as d 
  FROM testTable 
 GROUP BY d
 ORDER BY dateAdded DESC

Answer 3

use year and month function

 SELECT Year(dateAdded) as YearOfDate,Month(dateAdded) as MonthOfdate,
         , SUM(quantity) as Qty
      FROM testTable 
     GROUP 
        BY Year(dateAdded), Month(dateAdded) 
     ORDER  BY dateAdded DESC