here is what the help section has
The add prefix can be added to any Load, Select (SQL) or Map ... using statement in the script. It is only relevant during Partial Reload. During a partial reload the QlikView table, for which a table name is generated by the add load/add select statement (provided such a table exists), will be appended with the result of the add load/add select statement. No check for duplicates is performed. Therefore, a statement using the add prefix will normally include either a distinct qualifier or a where clause guarding duplicates. The map...using statement causes mapping to take place also during partial script execution.
The syntax is:
add [only] (loadstatement |selectstatement |mapstatement)
where:
only is an optional qualifier denoting that the statement should be disregarded during normal (non-partial) reloads.
Examples:
Tab1:
LOAD Name, Number FROM Persons.csv;
ADD LOAD Name, Number FROM newPersons.csv;
During normal reload, data is loaded from Persons.csv and stored in the QlikView table Tab1. Data from NewPersons.csv is then concatenated to the same QlikView table. See Concatenation.
During partial reload, data is loaded from NewPersons.csv and appended to the QlikView table Tab1. No check for duplicates is made.
Tab1:
SELECT Name, Number FROM Persons.csv;
ADD LOAD Name, Number FROM NewPersons.csv Where not exists(Name);
A check for duplicates is made by means of looking if Name exists in the previously loaded table data (see the function exists under exists(field [ , expression ] )).
During normal reload, data is loaded from Persons.csv and stored in the QlikView table Tab1. Data from NewPersons.csv is then concatenated to the same QlikView table.
During partial reload, data is loaded from NewPersons.csv which is appended to the QlikView table Tab1. A check for duplicates is made by means of seeing if Name exists in the previously loaded table data.
Tab1:
LOAD Name, Number FROM Persons.csv;
ADD ONLY LOAD Name, Number FROM NewPersons.csv Where not exists(Name);
During normal reload, data is loaded from Persons.csv and stored in the QlikView table Tab1. The statement loading NewPersons.csv is disregarded.
During partial reload, data is loaded from NewPersons.csv which is appended to the QlikView table Tab1. A check for duplicates is made by means of seeing if Name exists in the previously loaded table data.
