FETCH FIRST with PERCENT option is SQL standard that state limit count to be specified in a percentage in addition to specify it in exact count and listed as one of Major features simply not implemented yet in recent wiki page [1].
I implemented it by executing the query plan twice. One without limit filter to find the total number of row that will be feed to limit node so the exact limit count can be calculated and the query plan execute again with limit filter with newly calculated exact count .
