It's a way to filter rows of a table based on values of like variables in another table.
data casuser.baseball;
set sashelp.baseball;
run;
data casuser.where_table1;
set sashelp.baseball;
where team='Montreal';
keep team Name;
run;
data casuser.where_table2;
set sashelp.baseball;
where nhits >= 100;
keep name team nhits;
run;
proc cas;
table.copyTable /
casout={caslib="casuser", name="baseball_montreal", replace=TRUE},
table={caslib="casuser", name="baseball", whereTable={caslib="casuser" name="where_table1"}};
table.copyTable /
casout={caslib="casuser", name="baseball_nhits", replace=TRUE},
table={caslib="casuser", name="baseball", whereTable={caslib="casuser" name="where_table2"}};
table.fetch / table="baseball_montreal";
table.fetch / table="baseball_nhits";
quit;
You're right, though, the doc is light on the details, but I did find this one example with some explanation:
SAS Help Center: Filter Multiple Input Tables Based on Values in a whereTable
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