权限设置越复杂，所有 SQL 语句的开销就越大。简化通过 GRANT 语句建立的权限，可以使 MySQL 在客户端执行语句时减少权限检查开销。例如，如果您未授予任何表级或列级权限，服务器就无需检查 tables_priv 和 columns_priv 表的内容。类似地，如果您没有对任何账户设置资源限制，服务器就不需执行资源计数。如果您的语句处理负载非常高，可以考虑使用简化的授权结构来减少权限检查开销。The more complex your privilege setup, the more overhead applies to all SQL statements. Simplifying the privileges established by GRANT statements enables MySQL to reduce permission-checking overhead when clients execute statements. For example, if you do not grant any table-level or column-level privileges, the server need not ever check the contents of the tables_priv and columns_priv tables. Similarly, if you place no resource limits on any accounts, the server does not have to perform resource counting. If you have a very high statement-processing load, consider using a simplified grant structure to reduce permission-checking overhead.