Php ng>）

第四行向第一条指令添加了一个约束，仅选择

permission\u description

s

WHERE

role\u id=1

。因此，完整的说明是

从联接表（表4）中检索

权限描述
其中
角色\u id
为1

在简单的英语中，它的意思是：

检索角色“Admin”的权限描述

因此，查询的结果是：

Table 5: PERMISSION_DESCRIPTIONS of Admin
-----------------------------------------------
  permission_description
-----------------------------------------------
     Can create files
     Can edit files
     Can view files

希望这对你有帮助
 你真是太棒了，你一定会花点时间陪我。这真的很有帮助。。非常感谢。你真是太棒了，你一定会花点时间陪我。这真的很有帮助。。非常感谢。
roles
permissions
role_perms

SELECT t2.perm_desc FROM role_perm as t1
JOIN permissions as t2 ON t1.perm_id = t2.perm_id
WHERE t1.role_id = :role_id;

SELECT t2.perm_desc FROM role_perm as t1
JOIN permissions as t2 ON t1.perm_id = t2.perm_id AND t1.role_id=t2.role_id
WHERE t1.role_id = :role_id;

Table 1: ROLE
-----------------------------------------------
  role_id        role_description
-----------------------------------------------
     1               Admin
     2               Guest

Table 2: PERMISSIONS
-----------------------------------------------
  permission_id        permission_description
-----------------------------------------------
     1                 Can create files
     2                 Can edit files
     3                 Can view files

Table 3: ROLE_PERMISSIONS
-----------------------------------------------
  role_id        permission_id
-----------------------------------------------
     1                1
     1                2
     1                3
     2                3

SELECT t2.permission_description
FROM role_permissions as t1 JOIN permissions as t2
ON t1.permission_id = t2.permission_id
WHERE t1.role_id = 1

t1.permission_id = t2.permission_id

Table 4: Joint ROLE_PERMISSIONS and PERMISSIONS
------------------------------------------------------------------------
  role_id    permission_id    permission_id    permission_description
------------------------------------------------------------------------
     1             1               1              Can create files
     1             2               2              Can edit files
     1             3               3              Can view files
     2             3               3              Can view files

Table 5: PERMISSION_DESCRIPTIONS of Admin
-----------------------------------------------
  permission_description
-----------------------------------------------
     Can create files
     Can edit files
     Can view files