scope of a variable of bag in PIG

Question

I am beginner in PIG stuck on this problem

I have loaded a hive table using HCat storer in pig , which has a field current_hour: long

delta =
LOAD 'alpha.table1'
USING org.apache.hive.hcatalog.pig.HCatLoader();

now for some other calulation on a bag say beta I need to generate the current_hour from delta but I am not able to perform the operation

  grunt > gamma = FOREACH beta 
         GENERATE 
         x,
         y,
         delta::current_hour as current_hour;

Is there any way I can perform this calculation ?