在SQL Server 2000中，有教师表Teachers(TeacherID，Name，LeaderID)，其中TeacherID是主码，类型是长度为4的普通编码定长字符串，且每位是0～9的数字字符；Name的类型是长度为10的普通编码可变长字符串；LeaderID是每个教师的领导的TeacherID。
①写出创建Teachers表的SQL语句，要求语句中包含所有的约束。
②现要查询TeacherID为“1234”的教师的领导的TeacherID，请给出相应的SQL语句，要求只使用一条SQL语句实现，且此语句中不允许包含子查询。
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答 案：①create table Teachers( TeacherID char(4)check(TeacherID like" [0～9][0～9][0～9][0～9]") Name varchar(10) LeaderID char(4) primary key TeacherID foreign key LeaderlD references Teachers (TeacherID) ) ②select T2. LeaderID from Teachers as T1 join Teachers as T2 on T1.LeaderID=T2.TeacherID where T1.TeacherID=‘1234’
①create table Teachers( TeacherID char(4)check(TeacherID like" [0～9][0～9][0～9][0～9]")， Name varchar(10)， LeaderID char(4)， primary key TeacherID， foreign key LeaderlD references Teachers (TeacherID) ) ②select T2. LeaderID from Teachers as T1 join Teachers as T2 on T1.LeaderID=T2.TeacherID where T1.TeacherID=‘1234’