菜单id = 7的菜单项所拥有的按钮项
SELECT T1.*, TT.BUTTONID, TT.NAME FROM TBBUTTON T1 LEFT JOIN (SELECT * FROM TBMENUBUTTON T2 LEFT JOIN TBMENU T3 ON T2.MENUID = T3.ID WHERE T3.ID = 7 ) TT ON T1.ID = TT.BUTTONID
显示菜单项与按钮项的关联关系
原文：http://www.cnblogs.com/ShaYeBlog/p/4085690.html
