Question

I think it will be easiest to start with the table I have and the result I am aiming for.

Name | Date
A    | 03/01/2012
A    | 03/01/2012
B    | 02/01/2012
A    | 02/01/2012
B    | 02/01/2012
A    | 02/01/2012
B    | 01/01/2012
B    | 01/01/2012
A    | 01/01/2012

I want the result of my query to be:

Name | 01/01/2012 | 02/01/2012 | 03/01/2012
A    |     1      |     2      |     2
B    |     2      |     2      |     0

So basically I want to count the number of rows that have the same date, but for each individual name. So a simple group by of dates won’t do because it would merge the names together. And then I want to output a table that shows the counts for each individual date using php.

I’ve seen answers suggest something like this:

SELECT
  NAME,
  SUM(CASE WHEN GRADE = 1 THEN 1 ELSE 0 END) AS GRADE1,
  SUM(CASE WHEN GRADE = 2 THEN 1 ELSE 0 END) AS GRADE2,
  SUM(CASE WHEN GRADE = 3 THEN 1 ELSE 0 END) AS GRADE3
FROM Rodzaj
GROUP BY NAME

so I imagine there would be a way for me to tweak that but I was wondering if there is another way, or is that the most efficient?
I was perhaps thinking if the while loop were to output just one specific name and date each time along with the count, so the first result would be A,01/01/2012,1 then the next A,02/01/2012,2 – A,03/01/2012,3 – B,01/01/2012,2 etc. then perhaps that would be doable through a different technique but not sure if something like that is possible and if it would be efficient.

So I’m basically looking to see if anyone has any ideas that are a bit outside the box for this and how they would compare.

I hope I explained everything well enough and thanks in advance for any help.

Answer 1

You have to include two columns in your GROUP BY:

SELECT   name, COUNT(*) AS count
FROM     your_table
GROUP BY name, date

This will get the counts of each name -> date combination in row-format. Since you also wanted to include a 0 count if the name didn’t have any rows on a certain date, you can use:

SELECT     a.name,
           b.date,
           COUNT(c.name) AS date_count
FROM       (SELECT DISTINCT name FROM your_table) a
CROSS JOIN (SELECT DISTINCT date FROM your_table) b
LEFT JOIN  your_table c ON a.name = c.name AND 
                           b.date = c.date
GROUP BY   a.name, 
           b.date

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SQLFiddle Demo