某企业的数据库系统中有如下所示的员工关系和仓库关系,每个仓库可有多名员工,但只有一名负责人。员工关系(employee):仓库关系(warehouse):
- ACREATE TABLE (employee ID CHAR(2)NOTNULL UNIQUE, name CHAR(30)NOT NULL, address CHAR(40), principal ID CHAR(3));
- BCREATE warehouse(warehouse ID CHAR(2)PRIMARY KEY, name CHAR(30), address CHAR(40), principal ID CHAR(3));
- CCREATE TABLE warehouse(warehouse ID CHAR(2)PRIMARY KEY, name CHAR(30)NOT NULL, address CHAR(40), principal ID CHAR(3), FOREIGN KEY(principal ID)REFERENCES employee(employee ID));
- DCREATE TABIE warehouse(warehouse ID CHAR(2), name CHAR(30)NOT NULL, address CHAR(40), principal ID CHAR(3), PRIMARY REY(warehouse ID), FOREIGN KEY(employee ID)REFERENCES employee(employee ID));