解释该图。
两个实体:E1和E2
基数:
-从E1到E2(通过关系R):(6,50)
-从E2到E1(通过关系R):(3,5)
______ ^ ______
| E1 |___(6,50)____/R\____(3,5)___| E2 |
|______| \ / |______|
v
我应该强制执行基数,但是这本书没有深入探讨ASSERTION的细节。以下方法是否正确来强制执行所述基数?
CREATE ASSERTION assert
CHECK ( (SELECT COUNT(E1.ID) FROM E1) >= 6 AND
(SELECT COUNT(E1.ID) FROM E1) <= 60 AND
(SELECT COUNT(E2.ID) FROM E2) >= 3 AND
(SELECT COUNT(E2.ID) FROM E2) <= 5 );