Possible Bug in the Select InterfaceDist Command - mysql

Question

I am new to using SQL. I was wondering whether there could be a bug in this program.
/* Insert to interface table all atoms that have diffASA>0*/
insert into NinterfaceAtom(PDB,Chain,Residue,ResId,Symbol,atom,diffASA)
select PDB,Chain,Residue,ResId,Symbol,Atom,max(ASA)-min(ASA) from perAtomASA
group by PDB,Chain,Residue,ResId,Symbol,Atom
having stddev(ASA)>0;
/* Insert to interface table all atoms that have enough distance */
insert ignore into NinterfaceAtoms (PDB,Chain,Residue,ResId,Symbol,atom)
select asa.PDB,asa.Chain,asa.Residue,asa.ResId,asa.Symbol,dist.Atom from interfaceDist dist
inner join
perAtomASA asa
on
dist.PDB=asa.PDB and
dist.Chain=asa.Chain and
dist.ResId=asa.ResId and
dist.Symbol=asa.Symbol and
Seperated=0
I am just unsure why the programmmer before me put asa.PDB instead of dist.PDB in the inner join section.
I was thinking the eighth line needed to be changed from:
select asa.PDB,asa.Chain,asa.Residue,asa.ResId,asa.Symbol,dist.Atom from interfaceDist dist
to:
select dist.PDB,dist.Chain,dist.Residue,dist.ResId,dist.Symbol,dist.Atom from interfaceDist dist
Is that correct? Thanks.

Answer 1

You are joining asa and dist. It is perfectly logical that their values are checked to make sure only matching pairs will be in the result. So, unless you have a very good reason to think that in the line
dist.PDB=asa.PDB
you need dist.PDB instead of asa.PDB, the command looks to be correct. And if this would be correct
dist.PDB=dist.PDB
then it would be trivial and it would be pointless to have this part checked at all. When you identify bugs, you either need to see behavioral problems of the software, or to understand the code you are looking at.
EDIT
In the select clause one can use asa.PDB or dist.PDB, because the two are equal because of the on condition which ensured their equality. If the two are different, then the pair will not be in the result. So, in terms of values, it makes no difference. But if it is more intuitive to have dist.PDB in the select, then you might want to change it (there is no harm in it, because the value is exactly the same) so the code will be more readable and later, if the code is changed and the two will no longer have to be equal, you will not have new bugs out of the blue sky.