Even if two or more tables do not have exactly the same set of fields, it is still possible to force Qlik Sense to concatenate the two tables. This is done with the concatenate prefix in the script, which concatenates a table with another named table or with the last previously created table.
LOAD a, b, c from table1.csv;
concatenate LOAD a, c from table2,csv;
The resulting internal table has the fields a, b and c. The number of records in the resulting table is the sum of the numbers of records in table 1 and table 2. The value of field b in the records coming from table 2 is NULL.