1查询每门课的课号和先行课的先行课号(自我连接)
SELECT FIRST.CNO,SECOND.CPNO
FROM COURSE FIRST,COURSE SECOND
WHERE FIRST.CPNO=SECOND.CNO
2 查询每门课的课号,课名,先行课号,先行课名(自我连接)
1查询每门课的课号和先行课的先行课号(自我连接)
SELECT FIRST.CNO,SECOND.CPNO
FROM COURSE FIRST,COURSE SECOND
WHERE FIRST.CPNO=SECOND.CNO
2 查询每门课的课号,课名,先行课号,先行课名(自我连接)