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SQL AntiPatterns Presentation from MySQLConf 2009

44 pointsby jwinteralmost 16 years ago

3 comments

gcvalmost 16 years ago
Fascinating. I haven't finished reading the entire presentation yet, but I already stumbled on something.<p>The author lists a drawback of the first antipattern ("metadata tribbles"): a table split into multiples to keep its size down requires tricky querying, specifically, it requires a union across all splits (slide 10). It also requires extra effort to keep table structures synchronized (slide 11). Then, in a solution to his second antipattern ("entity-attribute-value"), he suggests doing something quite similar to his first antipattern: creating multiple tables with nearly identical columns and using a union to query across them (slides 27 and 28).<p>Hello? So to resolve antipattern 2 you just apply antipattern 1? This is why precisely why relational databases for most problems look like square pegs being hammered into round holes.<p>[EDIT] Not sure if it's worth finishing reading this presentation. Slide 56, a "solution" to the problem of storing a hierarchy in a relational database. Breadcrumbs. Not bad, except that the query now requires a "like" clause. Whoops, can't use an index on that column anymore! (Feel free to correct me if there exists a RDBMS which can use an index on a "like.") Hope the author doesn't mind a nice table scan on that query. He doesn't even mention this problem.
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snorkelalmost 16 years ago
I disagree with slides 20 - 30 (calling "entity-attribute-value" tables an antipattern). Variable attributes table not only gives you a lot of application flexibility but also helps performance in that you're not polluting your primary table with extraneous metadata columns that are hardly ever referenced. It doesn't surprise me that DB programmer would look at that and be offended that it's not purely referential -- not everything that happens in a database has to be referential to everything else. Sometimes databases are just dumb data stores. Not all problems are solved by "referential integrity"
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gchpacoalmost 16 years ago
I was expecting something more MySQL specific, and was pleasantly surprised. It's certainly worth thinking twice before violating any of these.