157.Examine the commands executed in the following sequence: 1: SQL> CREATE ROLE mgrrole; 2: SQL> G

本文探讨了一组Oracle数据库中角色权限的授予与使用案例。详细分析了mgrrole与ceo两个角色之间的权限授予过程,并指出了在角色间互相授权时可能产生的错误。通过此案例,读者可以了解Oracle数据库角色权限管理的基本原则。

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157.Examine the commands executed in the following sequence:

1: SQL> CREATE ROLE mgrrole;
2: SQL> GRANT create user,select any table,connect,resource TO mgrrole;
3: SQL> GRANT select,update ON sh.sales TO mgrrole;
4: SQL> CREATE ROLE ceo IDENTIFIED BY boss;
5: SQL> GRANT mgrrole,drop any table,create any directory TO ceo;
6: SQL> GRANT ceo TO mgrrole;

Which statement is true about the above commands?
A.The commands execute successfully.
B.Command 6 produces an error because of circular role grant.
C.Command 5 produces an error because a role cannot be granted to another role.
D.Command 3 produces an error because the MGRROLE role already contains system privileges.
E.The table created by HR remains and HR can grant the CREATE TABLE system privilege to other users.
答案:B
解析:
A:错误,这个命令是错误的,因为角色不能相互授予,这里第5部已经将mgrrole授予了ceo,第六部又将ceo授予了mgrrole
B:正确
C:错误,角色是可以包含角色的
D:错误,虽然角色已经包含了对应的权限,但是还是可以单独授予该权限的,这个时候必须角色和权限都回收,该权限才会回收
E:错误,这里没有with admin option,因此hr不具备授予其他用户的权限
Gas Metal Arc Welding (GMAW) is a widely used welding process in which a consumable metal wire electrode is fed into a weld pool to join two or more metal parts together. During the welding process, the electrode melts and forms a molten metal pool, which then cools and solidifies to form a welded joint. One way to analyze the GMAW process is to examine the metal-transfer images that are generated during welding. Metal-transfer images are high-speed photographs or videos of the GMAW process that capture the behavior of the molten metal as it is transferred from the electrode to the workpiece. Analyzing these images can provide insights into the physical processes that occur during welding, such as droplet detachment, droplet formation, and arc behavior. There have been several studies that have analyzed metal-transfer images in the GMAW process. One such study was conducted by Liu et al. (2017), who used high-speed photography to capture metal-transfer images during GMAW of aluminum alloys. They found that the droplet detachment frequency was influenced by the welding current, and that there was a critical current level above which the droplet detachment frequency increased dramatically. Another study by Liao et al. (2019) analyzed metal-transfer images during GMAW of high-strength steel. They found that the droplet transfer mode shifted from globular to spray transfer as the welding current increased, and that the formation of an unstable arc affected the droplet detachment process. Other researchers have used image processing techniques to analyze metal-transfer images. For example, Zhang et al. (2019) developed an algorithm to automatically detect and track the movement of droplets in metal-transfer images during GMAW. They found that the droplet size and transfer frequency were affected by the welding current and the wire feed speed. Overall, the analysis of metal-transfer images in the GMAW process is an active area of research that has the potential to improve our understanding of the physical processes that occur during welding. By studying metal-transfer images, researchers can gain insights into the factors that affect droplet detachment, droplet formation, and arc behavior, which can in turn help to optimize the welding process for different materials and applications.
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