Comments on: SQL functions in WHERE clauses are evil http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/ Thoughts from the nice people at Codevader :) Sat, 19 May 2012 20:21:33 +0000 http://wordpress.org/?v=2.6.2 By: Mark http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/#comment-736 Mark Mon, 15 Dec 2008 17:24:15 +0000 http://blog.codevader.com/?p=67#comment-736 I was thinking exactly the same thing as Rich: why no index on the DAYOFMONTH function? That's clearly the cleanest solution. I never thought that MySQL wouldn't support it, reminding us all about what a toy database it really is. I was thinking exactly the same thing as Rich: why no index on the DAYOFMONTH function? That’s clearly the cleanest solution. I never thought that MySQL wouldn’t support it, reminding us all about what a toy database it really is.

]]> By: Maurício Linhares http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/#comment-734 Maurício Linhares Wed, 10 Dec 2008 18:06:51 +0000 http://blog.codevader.com/?p=67#comment-734 Hey Rich, This is a new one for me, didn't knew that other databases supported this kind of feature, thanks for the tip :) Hey Rich,

This is a new one for me, didn’t knew that other databases supported this kind of feature, thanks for the tip :)

]]> By: Rich Cavanaugh http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/#comment-733 Rich Cavanaugh Wed, 10 Dec 2008 15:46:45 +0000 http://blog.codevader.com/?p=67#comment-733 A better mantra may be "SQL functions in where clauses are evil when using toy database software." On PostgreSQL you're able to define an index based on an SQL function. I've used it to deal with a case almost identical to your example. You can see some example code here http://pastie.textmate.org/private/y8cfsxezf2f8x2tvrishq There's explain output at the bottom of that pastie. Note specifically the "Bitmap Index Scan" and "Index Cond" lines. It's worth noting that Drizzle has this feature in a round about way via a feature called virtual columns. A better mantra may be “SQL functions in where clauses are evil when using toy database software.”

On PostgreSQL you’re able to define an index based on an SQL function. I’ve used it to deal with a case almost identical to your example.

You can see some example code here http://pastie.textmate.org/private/y8cfsxezf2f8×2tvrishq There’s explain output at the bottom of that pastie. Note specifically the “Bitmap Index Scan” and “Index Cond” lines.

It’s worth noting that Drizzle has this feature in a round about way via a feature called virtual columns.

]]> By: nick http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/#comment-732 nick Wed, 10 Dec 2008 06:56:55 +0000 http://blog.codevader.com/?p=67#comment-732 How much of an issue is this really? If I run your example query against a table with 180,000 records, it still only takes around 0.3 seconds - hardly a huge wait. If the query was getting run thousands of times a day, then by all means, let's optimise. But if, as in your example, we're doing this once a day to send birthday wishes, then our optimising time is better spent elsewhere. How much of an issue is this really? If I run your example query against a table with 180,000 records, it still only takes around 0.3 seconds - hardly a huge wait.

If the query was getting run thousands of times a day, then by all means, let’s optimise. But if, as in your example, we’re doing this once a day to send birthday wishes, then our optimising time is better spent elsewhere.

]]> By: Marcelo http://blog.codevader.com/2008/12/10/sql-functions-in-where-clauses-are-evil/#comment-731 Marcelo Wed, 10 Dec 2008 01:41:20 +0000 http://blog.codevader.com/?p=67#comment-731 Great! Thanks for the tip. Great! Thanks for the tip.

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