Q&A for professional and enthusiast programmers
SELECT d, SUM(h2) OVER (ORDER BY d) AS h2, SUM(hsqldb) OVER (ORDER BY d) AS hsqldb, SUM(derby) OVER (ORDER BY d) AS derby FROM ( SELECT CAST(CreationDate AS DATE) AS d, COUNT(CASE WHEN Tags LIKE '%<h2>%' THEN 1 END) AS h2, COUNT(CASE WHEN Tags LIKE '%<hsqldb>%' THEN 1 END) AS hsqldb, COUNT(CASE WHEN Tags LIKE '%<derby>%' THEN 1 END) AS derby FROM Posts GROUP BY CAST(CreationDate AS DATE) ) AS DailyPosts ORDER BY d ASC