更新整数列中的特定位 [英] update specific bit in integer column

问题描述

我有一个mysql表，其中用户权限存储为位掩码:

I have a mysql table where user permissions are stored as a bitmask:

|user   | permissions |
| Admin | 31          |
| User  | 13          |

           16 8  4  2  1
Admin ->   1  1  1  1  1  -> 16 + 8 + 4 + 2 + 1 -> 31
User  ->   0  1  1  0  1  ->  8 + 4 + 1 -> 13

现在，我想使用SQL查询为每个用户添加权限. 假设我想为所有人添加权限16，而无需另外修改.

Now I want to add a permission for every user with an sql query. Let's say I want to add the permission 16 for everyone without modifying another bit.

 UPDATE users SET permission = ????

我该怎么做?

推荐答案

要添加权限16，您只需说

To add permission 16, you just say

UPDATE users SET permission = permission | 16;

按位或运算符将打开位.要关闭它们，请使用AND操作加上您要关闭的位的补码:

The bitwise OR operator will turn bits on. To turn them off, use a AND operation with the complement of the bit you want off:

UPDATE users SET permission = permission & ~16

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