Missed the (obvious) MySQL reference in the title, sorry.
The data in the date field is in the format dd:mm:yyyy, which indicates that it is _not_ a datetime field (so it must be a text field). In this case andreas1234567's approach would not work.
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Ignorance killed the cat, curiosity was framed.
I was referring to the fact that the target was asked to be of integer type, but I see your point about the source. Probably a merge between your solution and andreas1234567's would do.