### 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 is the percentage of molecules that are carcinogenic? Please provide your answer as a percentage with three decimal places.

### Extra Knowledge:
label = '+' mean molecules are carcinogenic; percentage = DIVIDE(SUM(label = '+'), COUNT(molecule_id)) as percent
SELECT ROUND(CAST(COUNT(CASE WHEN T.label = '+' THEN T.molecule_id ELSE NULL END) AS REAL) * 100 / COUNT(T.molecule_id),3) FROM molecule t