对于基于sql的数据库:

Not taking advantage of CLUSTERED INDEXES or choosing the wrong column(s) to CLUSTER. Not using a SERIAL (autonumber) datatype as a PRIMARY KEY to join to a FOREIGN KEY (INT) in a parent/child table relationship. Not UPDATING STATISTICS on a table when many records have been INSERTED or DELETED. Not reorganizing (i.e. unloading, droping, re-creating, loading and re-indexing) tables when many rows have been inserted or deleted (some engines physically keep deleted rows in a table with a delete flag.) Not taking advantage of FRAGMENT ON EXPRESSION (if supported) on large tables which have high transaction rates. Choosing the wrong datatype for a column! Not choosing a proper column name. Not adding new columns at the end of the table. Not creating proper indexes to support frequently used queries. creating indexes on columns with few possible values and creating unnecessary indexes. ...more to be added.

a)在字符串中硬编码查询值 b)将数据库查询代码放在Windows窗体应用程序的“OnButtonPress”操作中

两者我都见过。

当查询在您的开发机器上运行得如此之快时，一旦您向应用程序抛出一些流量，查询就会崩溃并阻塞，这要归咎于db引擎。

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

对于基于sql的数据库:

Not taking advantage of CLUSTERED INDEXES or choosing the wrong column(s) to CLUSTER. Not using a SERIAL (autonumber) datatype as a PRIMARY KEY to join to a FOREIGN KEY (INT) in a parent/child table relationship. Not UPDATING STATISTICS on a table when many records have been INSERTED or DELETED. Not reorganizing (i.e. unloading, droping, re-creating, loading and re-indexing) tables when many rows have been inserted or deleted (some engines physically keep deleted rows in a table with a delete flag.) Not taking advantage of FRAGMENT ON EXPRESSION (if supported) on large tables which have high transaction rates. Choosing the wrong datatype for a column! Not choosing a proper column name. Not adding new columns at the end of the table. Not creating proper indexes to support frequently used queries. creating indexes on columns with few possible values and creating unnecessary indexes. ...more to be added.

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。