How not to design a database.

I work in education/consulting and it is one of the example of what I have seen (during this year only). And, I’m not talking about small fries but companies with LOTS of digits. I said: Oh, this data it’s wrong, it shows $xxxxxxx and they tell me, yes, the information is right.

Database’s mistakes

• Tables with a prefix to say that it is a table, example TABLE_CUSTOMER or TBL_CUSTOMER. (ed: Sheesh, I know that it’s a table!.)
• Cryptic tables, TBL23. (ed: WTF?. SAP, I am watching you.)
• Using the tables as non relational, (you will get a cookie if you can find the mistake):

• Varchar as index (ed: it is extra heretical)

• Inconsistent table. (ed: However, LEFT JOIN saves the day. Pro-tip: FOREIGN-KEY is your friend, your pal, your cuate!.)
• Pasword in plain text. (ed: even md5 is way better)
• Installing Oracle by following the Database Administrator’s Guide

• Age as a integer. (ed: now()-datefield() will do the damn trick!)
• Or, Age as a varchar
• Column with varchar with padding for space. Because char is for cowards!
• Date column as varchar.
• Using nchar and nvarchar for everything.
• Float instead of money. Why? because the architect says that float is more efficient. (tips: extra heretical too)
• Blob
• More blob. Database loves blob so much.
• Using Trigger for reporting. (ed: please, don’t ask)
• Trust me, you could do 2 inserts without transition. What could go wrong?.
• MyISAM because it’s the fastest. (ed: lie, Blackhole is the fastest).
• The Log file is too big, it’s time to delete it manually. Why? Who cares, it is only the log file.
• No Primary Key?. Why?. Because reasons.
• A table with 30 columns and 30 indexes.
• Join without using any index
• Select to the biggest table of the system without filtering. We need to read 100 million rows to show a 30 lines report!.
• Oracle is cheaper and you can save money $$$$$ (tips: no, it’s not!)
• My IBM vendor tells me that IBM is cool.
• Replication is funny
• Bokup? what is that?.
• Replication never fails.
• Cursor for everything, what could go wrong?.
• Who needs parametric query?.
• Varchar(1) for Y/N fields (and no nulls or empty). Why?, because char is for cowards too.
• My database server needs more CPU, not ram!.
• We don’t need a new table but more columns. Invoices, who purchase more than 3 products at once?