㈠ 1. 已知教学管理数据库（jxgl.dbc）中有三张表，定义如下：1. 已知教学管理数据库（jxgl.dbc）中有三张表，
1.select xh,kcdh,cj from cj where cj>=70 and cj<=80 order by cj desc
2.select xs.xh,xm from xs,cj where kcdh="C2" and xs.xh=cj.xh order by xs.xh
3. select xs.xh,xm,kcm,cj from xs,kc,cj where xs.xh=cj.xh and kc.kcdh=cj.kcdh
4.select xh,xm,xb from xs where xm like "方%"
5.select kcdh,cj from xs,cj where xm="方华"