NAME SYMBOL KEYBOARD FORM CHE UNION UNION 并 INTERSECT 交 DIFFERENCE - MINUS 差 //前三類是要條件的，就像矩陣運(yùn)算一樣 條件：大概意思是 狗只能跟狗比，不能跟貓比 PRODUCT * TIMES 笛卡兒積 2。 NATIVE RELATIONAL OPERATIONS
PROJECT R[] R[] 取其中幾列 SELECT R WHERE C R WHERE C 就像SQL中的select * from C 一樣 JOIN JOIN 合并：所有“共有列”一樣的record才保留 DIVISION / DIVIDBY 除以 // If the table R is defined by R = T*S,then it is true that T = R DIVIDBY S.
EXAMPLE 2.96(表格跟見(jiàn)上篇文章） 0 := ORDERS --alias GET cids of customers who order all products that anybody orders.This is division again,and the divisor,the list of “all” products,must be projected from ORDERS rather than PRODUCTS. 0[cid,pid]/0[pid]
