Can we execute a sql statement from iOS to run a query?

[SeanNakasone]

Can we execute a sql statement from iOS to run a query?
I've investigated AGSFindTask, but is seems like this is not powerful enough.
I would like to run a statement like "select a, b from mytable where a = 'the' and b = 'quick' "
It seems like I can use AGSQueryTask with the use of AGSRelationshipQuery for the parameters.
What is AGSRelationshipQuery.definitionExpression used for?  Can this be set to a sql statement?

Also, if I want to query:
http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Demographics/ESRI_Census_USA/MapServer/3

How do I know what the underlying tablename is?

[SeanNakasone]

I think I found it.  AGSQuery.where property.

I'm guessing we can't issue an entire select statement with AGSQueryTask.