使用Excel存储(大量)数据。

我曾见过一些公司拥有数千行并使用多个工作表(由于以前版本的Excel的行数限制为65535)。

Excel非常适合用于报告、数据演示和其他任务，但不应被视为数据库。

不使用参数化查询。它们在停止SQL注入时非常方便。

这是一个不消毒输入数据的具体例子，在另一个回答中提到过。

不了解DBMS的工作原理。

如果不了解离合器的工作原理，你就不能正确地驾驶变速杆。如果不了解实际上只是在硬盘上写入文件，就无法理解如何使用数据库。

具体地说:

Do you know what a Clustered Index is? Did you think about it when you designed your schema? Do you know how to use indexes properly? How to reuse an index? Do you know what a Covering Index is? So great, you have indexes. How big is 1 row in your index? How big will the index be when you have a lot of data? Will that fit easily into memory? If it won't it's useless as an index. Have you ever used EXPLAIN in MySQL? Great. Now be honest with yourself: Did you understand even half of what you saw? No, you probably didn't. Fix that. Do you understand the Query Cache? Do you know what makes a query un-cachable? Are you using MyISAM? If you NEED full text search, MyISAM's is crap anyway. Use Sphinx. Then switch to Inno.

忘记在表之间建立关系。我记得当我刚开始在我现在的雇主工作时，我不得不清理这些东西。

开发人员所犯的关键数据库设计和编程错误

Selfish database design and usage. Developers often treat the database as their personal persistent object store without considering the needs of other stakeholders in the data. This also applies to application architects. Poor database design and data integrity makes it hard for third parties working with the data and can substantially increase the system's life cycle costs. Reporting and MIS tends to be a poor cousin in application design and only done as an afterthought. Abusing denormalised data. Overdoing denormalised data and trying to maintain it within the application is a recipe for data integrity issues. Use denormalisation sparingly. Not wanting to add a join to a query is not an excuse for denormalising. Scared of writing SQL. SQL isn't rocket science and is actually quite good at doing its job. O/R mapping layers are quite good at doing the 95% of queries that are simple and fit well into that model. Sometimes SQL is the best way to do the job. Dogmatic 'No Stored Procedures' policies. Regardless of whether you believe stored procedures are evil, this sort of dogmatic attitude has no place on a software project. Not understanding database design. Normalisation is your friend and it's not rocket science. Joining and cardinality are fairly simple concepts - if you're involved in database application development there's really no excuse for not understanding them.

这之前已经说过了，但是:索引，索引，还是索引。我见过许多性能不佳的企业web应用程序，它们通过简单地进行一些分析(查看哪些表被频繁访问)，然后在这些表上添加索引来解决问题。这甚至不需要太多的SQL编写知识，而且回报是巨大的。

Avoid data duplication like the plague. Some people advocate that a little duplication won't hurt, and will improve performance. Hey, I'm not saying that you have to torture your schema into Third Normal Form, until it's so abstract that not even the DBA's know what's going on. Just understand that whenever you duplicate a set of names, or zipcodes, or shipping codes, the copies WILL fall out of synch with each other eventually. It WILL happen. And then you'll be kicking yourself as you run the weekly maintenance script.

最后:使用清晰、一致、直观的命名约定。与一段编写良好的代码应该是可读的一样，一个好的SQL模式或查询应该是可读的，并且实际上告诉您它在做什么，甚至没有注释。六个月后，当你不得不对桌子进行维护时，你会感谢自己的。“选择account_number, billing_date FROM national_accounts”比“选择ACCNTNBR, BILLDAT FROM NTNLACCTS”更容易使用。