rel-ops.txt

ssd7数据库的联系一到练习三

1.Relational operations I used:
 select,project and join. 
2.Roles of each operation in my query:
I use select operation to retrieve the rows which I want and the conditions are expressed in where clause. 
I use project to limit the columns to be displayed. 
I use join operation to jion two ralative tables on condition so the information in the two tables can be retrieved.