This will give you the count of records where id=16
To combine the two tables, and get a percentage, there's quite a few different methods you could use - one example - which is possibly the worst, is:
SELECT ([T2]/[T1])*100 As Percentage
FROM (SELECT Count(id) AS T1 from Table1 having id=16) As Tbl1,
SELECT Count(id) AS T2 from Table2 having id=16) AS Tbl2;
Just as a note on calculating the percentages - you may prefer to multiply rather than divide, as dividing is a more complex command at machine level.
Of course, in a simple calculation it will only result in the answer taking a nanosecond or two longer, and the majority of compilers change division to multiplication, but mentioning it does pad out this reply which would otherwise just be me posting the code
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