Working with CASE statement in Calculated Attribute

Hi All

I am trying to apply the same logic which I used for IF statement for CASE also,I am creating calculated attribute for Age group using IF it is working,but

the CASE functionality is not working.I followed modelling guide SPS4 to define below logic.

case("AGE" >=30 AND<=35,'30-35', >=35 AND <=40,'35-40', >=40 AND <=45,'40-45','50-55' )

Is it that we can't write conditions in CASE , or I am using wrong syntax.Also can we use SQL predefined functions while creating calculated attribute or we can only use which are there in the window ,because there I could not see any functions for Concatenate ,which is very basic need in String functions.Request your Ideas.

Thanks

Santosh Varada