Question

how can I join two tables and make the second optional?

SELECT t1.title,SUM(t2.seconds) AS seconds 
FROM operation t1 
  LEFT JOIN workhours t2 ON t1.id = t2.pid AND t1.status='0' 
ORDER BY t1.tstamp DESC

This query shows only one result but there is a second one withour any worktime on it. How can I make sure that the data from t1 will always be displayed even when there is nothing in t2?

Answer 1

You need to add GROUP BY t1.title:

SELECT t1.title,SUM(t2.seconds) AS seconds 
FROM operation t1 LEFT JOIN workhours t2 ON t1.id = t2.pid AND t1.status='0' 
GROUP BY t1.title
ORDER BY t1.tstamp DESC

In general, if title is not unique, you should group by unique key.