For example, assume the membership in force for 1 year. ID 101. The member join 1 jan 2010 as level 1 then the start date for this member is 1 jan 2010 and theoritically end at 1 jan 2011. On 1 jul 2010, ID 101 upgrade to level 2 so for level 1 it effective end at 1 Jul 2010 and continue the remaining period in level 2 effective from 1 Jul 2010 until 1 Jan 2011. So basically, the resulting table for each level, it has the "revised expiry" date. In this example, after the revision, level 1 start on 1 jan 2010 and end at 1 jul 2010 while level 2 start on 1 Jul 2010 and end at 1 jan 2011 Thanks!
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