MySql PHP select count of distinct values from comma separated data (tags)

Question

How can I select the count of distinct values from data that is stored as comma separated values in MySql? I\'ll be using PHP to output the data from MySql in the end.

Answer 1

This should work:

SELECT tag, count(0) count FROM (
    SELECT tOut.*, REPLACE(SUBSTRING(SUBSTRING_INDEX(tags, ',', ocur_rank), LENGTH(SUBSTRING_INDEX(tags, ',', ocur_rank - 1)) + 1), ',', '') tag
      FROM (
        SELECT @num_type := if(@id_check = tY.id, @num_type + 1, 1) AS ocur_rank, @id_check := tY.id as id_check, tY.*
          FROM (
            SELECT LENGTH(tags) - LENGTH(REPLACE(tags, ',', '')) AS num_ocur, id, tags FROM tablename
          ) tX
          INNER JOIN (SELECT LENGTH(tags) - LENGTH(REPLACE(tags, ',', '')) AS num_ocur, id, tags FROM tablename) tY
          INNER JOIN (SELECT @num_type := 0, @id_check := 'some_id') tZ
       ) tOut
     WHERE ocur_rank <= num_ocur + 1
) tempTable GROUP BY tag ORDER BY count DESC;

Replace "tablename" with the name of your table.

This answer was derived from a solution by Jesse Perring posted on this page:

http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#c12113