### Database Schema:
CREATE TABLE tags (
	index	INTEGER	NULL	PRIMARY KEY,
	id	INTEGER	NULL,
	tag	TEXT	NULL,
	foreign key (id) references torrents (id)
);

CREATE TABLE torrents (
	groupName	TEXT	NULL,
	totalSnatched	INTEGER	NULL,
	artist	TEXT	NULL,
	groupYear	INTEGER	NULL,
	releaseType	TEXT	NULL,
	groupId	INTEGER	NULL,
	id	INTEGER	NULL	PRIMARY KEY
);

### User's Query:
An American rapper '2Pac' released his first solo album in 1991, how many years have passed until his next album was released?

### Extra Knowledge:
2Pac is an artist; album refers to releaseType; groupYear = 1991; SUBTRACT(groupYear = 1991, groupYear where releaseType = 'album' LIMIT 1 OFFSET 1);
SELECT ( SELECT groupYear FROM torrents WHERE artist LIKE '2Pac' AND releaseType LIKE 'album' ORDER BY groupYear LIMIT 1, 1 ) - groupYear FROM torrents WHERE artist LIKE '2Pac' AND releaseType LIKE 'album' AND groupYear = 1991