TIMEDIFF(endDate, startDate)
outputs in DateTime format, so flat that to timestamp and devide by (60*60)
SELECT (UNIX_TIMESTAMP(TIMEDIFF(endDate, startDate))/(60*60)) AS hours_difference
FROM tasks
Edit: Alternatively,TimestampDiff may also provide a valid solution in more elegant way providing its example:
SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01');
And your solution can be:
SELECT TIMESTAMPDIFF(HOUR, startDate, endDate) AS hours_different
FROM tasks
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