Database development mistakes made by application developers

What are common database development mistakes made by application developers?

Forgetting to set up relationships between the tables. I remember having to clean this up when I first started working at my current employer.

Not using indexes.

Not doing the correct level of [normalization][1]. You want to make sure that data is not duplicated, and that you are splitting data into different as needed. You also need to make sure you are not following normalization *too* far as that will hurt performance.


[1]:

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In my experience:<br/>
Not communicating with experienced DBAs.<br/>

Blaming the db engine when the query that ran sooo fast on your development machine blows up and choke once you throw some traffic at the application.

1. Not using version control on the database schema
2. Working directly against a live database
3. Not reading up and understanding more advanced database concepts (indexes, clustered indexes, constraints, materialized views, etc)
4. Failing to test for scalability ... test data of only 3 or 4 rows will never give you the real picture of real live performance

Number one problem? They only test on toy databases. So they have no idea that their SQL will crawl when the database gets big, and someone has to come along and fix it later (that sound you can hear is my teeth grinding).

Treating the database as just a storage mechanism (i.e. glorified collections library) and hence subordinate to their application (ignoring other applications which share the data)

Not using parameterized queries. They're pretty handy in stopping [SQL Injection](

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).

This is a specific example of not sanitizing input data, mentioned in another answer.