The plain functions used to cast the datatype of a column in the previous section point out one issue to be aware of for RAQL queries: in many cases, the RAQL Engine that runs the query has no datatype information for a given column. This is particularly true for data in CSV or XML formats.

When datatype information is not available, the RAQL Engine derives a schema based on the first row of data. For most purposes, this means that the data is treated as a string unless you explicitly cast it to another datatype.

Instead of using casting functions, you can provide datatype information for datasets in your mashup. See Providing Dataset Path and Datatype Information in a Schema for more information.