@a - connection_id()
3
i
1
2
i @vv1:=if(sv1.i,1,0) @vv2:=if(sv2.i,1,0) @vv3:=if(sv3.i,1,0) @vv1+@vv2+@vv3
1 1 0 1 2
2 1 0 0 1