using "apply map" to map the column names.Please help me to undersand with examples
do you mean renaming column names?
How to Rename Fields
Could you please give an example of what you are trying to achieve?
Please include example data / source data.
rowno() as field1,
rand()*100 as field2,
1 as field3
if you stop the script here you get
Mapping Load * inline [
Rename Fields using FieldNameMap;
Retrieving data ...