认为他们是dba和数据建模师/设计人员，而他们在这些领域没有任何正式的灌输。 认为他们的项目不需要DBA，因为这些东西都很简单/琐碎。 未能正确区分应该在数据库中完成的工作和应该在应用程序中完成的工作。 未验证备份，或未备份。 在他们的代码中嵌入原始SQL。

使用Access而不是“真正的”数据库。有很多很棒的小型甚至免费的数据库，比如SQL Express、MySQL和SQLite，它们可以更好地工作和扩展。应用程序通常需要以意想不到的方式进行扩展。

没有做正确的标准化。您希望确保数据没有重复，并且根据需要将数据分割为不同的数据。您还需要确保不要过于遵循规范化，否则会损害性能。

如果您正在使用复制(MySQL)，以下函数是不安全的，除非您正在使用基于行的复制。

USER(), CURRENT_USER() (or CURRENT_USER), UUID(), VERSION(), LOAD_FILE(), and RAND()

参见:http://dev.mysql.com/doc/refman/5.1/en/replication-features-functions.html

在运行DELETE查询之前没有执行相应的SELECT查询(特别是在生产数据库上)!

I think the biggest mistakes that all developers and DBAs do is believing too much on conventions. What I mean by that is that convention are only guide lines that for most cases will work but not necessarily always. I great example is normalization and foreign keys, I know most people wont like this, but normalization can cause complexity and cause loss of performance as well, so if there is no reason to move a phone number to a phones table, don't do it. On the foreign keys, they are great for most cases, but if you are trying to create something that can work by it self when needed the foreign key will be a problem in the future, and also you loose performance. Anyways, as I sad rules and conventions are there to guide, and they should always be though of but not necessarily implemented, analysis of each case is what should always be done.