selectClause in ds.xml causes datasource error

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1. SmartClient Version v10.0p_2015-03-14/Power Edition Deployment
(built 2015-03-14)

2. I have a selectClause in myds.ds.xml that works correctly. Its got some custom MySQL sql. It works however when I replace a sum(myfield) with
sum( if (myfield <= 100, 100,0)) I get errors loading the data source. I checked the sql via the MySQL console and it runs correctly so I believe the syntax is correct.

So my question is should I expect this work, or is there perhaps some special characters or keywords that need to be escaped or something ??

Thanks