Question

I have an issue where I would like to look for statements in a single column and each time I find them insert a new column into the mix. Im using a mysql database.

For example say I have data like this

  Class     Sub
  -----------------
    1       math       
    1       tech 
    2       math
    2       english
    3       math

I would like the data to be output like this:

Class    math  tech english
---------------------------
    1      Y     Y     N
    2      Y     N     Y
    3      Y     N     N

I am trying to use CASE statements to find the values in the column, but the problem is that it will only return one result in the column for the value it finds, and i end up getting the same class repeated with a case statement for each column. Combining the case statements wont work as that still gives me a single column.

Answer 1

You need to wrap the CASE expression in an aggregate and add a GROUP BY. In this case MAX will work as alphabetically Y comes after N

(SQL Fiddle Demo)

SELECT class,
       MAX(CASE
             WHEN ( community_id = 'Math' ) THEN 'Y'
             ELSE 'N'
           END)  AS Math,
       MAX (CASE
              WHEN ( community_id = 'tech' ) THEN 'Y'
              ELSE 'N'
            END) AS tech,
       MAX (CASE
              WHEN ( community_id = 'english' ) THEN 'Y'
              ELSE 'N'
            END) AS english
FROM   x_class_community
GROUP  BY class