Set up a log system

I would like to set up a log system in which all user changes to the various queries are saved.

Here’s an example
$user changed in area $area [$timestamp]:
$variable1 from value1 to value2
$variable2 from value2 to value4
$variable3 from value3 to value6
$variable4 from value5 to value8

Preferably with just one query.

How can I implement this?