This is the IBM Informix Spatial DataBlade on line reference manual. This manual is really well done. I have to commend IBM for that. It is amazing how much in syntax IBM SpatialDataBlade is to PostGIS. If you are a PostGIS, SQL Server 2008 Spatial or other OGC compliant spatial database user, you will find this manual useful as well.
It is chuck full of examples of use of each SFSQL function plus diagrams demonstrating spatial relationships and going into lengthy detail about what each spatial relationship/function does. Again - Well done IBM.