Your commend should be like sting
If you Use "SELECT sum(a1) from num_emp" then a1 is a part of string, not connection with cell value.
You should do your string from parts like: "SELECT sum(" & a1.value & ") from num_emp"
Of course sum with one cell can't work properly.
Then i guess:
"SELECT field from num_emp where field = " & sum(a1:a4)
Check if that make sense on your site. Better to check your select on DB first, before you translate to VBA sting.
Regards