No the data is not loss when we comment the fields the purpose is to commenting is just to remove unwanted fields and for memory utilization and sometimes to remove synthetic keys and to avoid circular loop
like i have two tables
table1:
load Productid,Orderid,Qty,Productname
from table1;
table2:
load Productid,Orderid,Productname,orderdate
from table 2;
when i reload it creating a synthetic key the purpose here to remove synthetic key for this
i load all data from table 1 and also add field (Productid &'|'& Orderid) as Link
and in table 2 i also add field (Productid &'|'& Orderid) as Link
and comment Productid,Orderid and rest of field i fetch
so doing this after reload my table would be link with each other using a field Link
similarly when three or more tables are linked to each pther then create a circular loop to avoid it using alias menas change the name of link or you can make a composite field
however if your data in two tables become unique with several fields the use autonumberhash256() function see it on help side it compact the memory and generate a unique no.
