I make e-commerce medial pharmacy online 
there I need SALTS searching men's formula of the medicine
suppose Digene is tablet and its formula is 
atenol 250mg 
amlodipine 350mg 
now i insert a table in record 
tbl_salts
pid  sid
1      1 (atenol 250mg )
1      2 (amlodipine 350mg )
now this forluma also relted other medicine 
like calpon  conatine only amlodipine 350mg
now my table is 
pid  sid
1      1 (atenol 250mg )
1      2 (amlodipine 350mg )
2      2 (amlodipine 350mg )  
like so on 
pid  sid
1      1 (atenol 250mg )
1      2 (amlodipine 350mg )
2      2 (amlodipine 350mg )  
3      1 (atenol 250mg )
4      1 (atenol 250mg )
4      2 (amlodipine 350mg )
now if the user select PID one 
Digene 
so it show aptitude also
4      1 (atenol 250mg )
4      2 (amlodipine 350mg )
not  show PID 2 and 3 because it is not an exact formula