### Database Schema:
CREATE TABLE connected (
	atom_id	TEXT	NOT NULL	PRIMARY KEY,
	atom_id2	TEXT	NOT NULL	PRIMARY KEY,
	bond_id	TEXT	NULL	DEFAULT NULL,
	foreign key (atom_id2) references atom (atom_id),
	foreign key (atom_id) references atom (atom_id),
	foreign key (bond_id) references bond (bond_id)
);

CREATE TABLE atom (
	atom_id	TEXT	NOT NULL	PRIMARY KEY,
	molecule_id	TEXT	NULL	DEFAULT NULL,
	element	TEXT	NULL	DEFAULT NULL,
	foreign key (molecule_id) references molecule (molecule_id)
);

CREATE TABLE bond (
	bond_id	TEXT	NOT NULL	PRIMARY KEY,
	molecule_id	TEXT	NULL	DEFAULT NULL,
	bond_type	TEXT	NULL	DEFAULT NULL,
	foreign key (molecule_id) references molecule (molecule_id)
);

CREATE TABLE molecule (
	molecule_id	TEXT	NOT NULL	PRIMARY KEY,
	label	TEXT	NULL	DEFAULT NULL
);

### User's Query:
What percentage of bonds have the most common combination of atoms' elements?

### Extra Knowledge:
DIVIDE(COUNT(bond_id), COUNT(atom_id where MAX(COUNT(atom_id)) ))
SELECT CAST((SELECT COUNT(T1.atom_id) FROM connected AS T1 INNER JOIN bond AS T2 ON T1.bond_id = T2.bond_id GROUP BY T2.bond_type ORDER BY COUNT(T2.bond_id) DESC LIMIT 1 ) AS REAL) * 100 / ( SELECT COUNT(atom_id) FROM connected )