With reference to Qlikview help!!
Join:It combines the two tables into single table based on the key column.(result as single table)
Keep: the two tables are not joined and will be kept in QlikView as two separately named tables.(Two Tables)
The keep prefix must be preceded by one of the prefixes inner, left or right.
When we go for keep:
In many cases joins will result in very large tables. One of the main features of QlikView is its ability to make associations between multiple tables instead of joining them, which greatly reduces memory usage, increases processing speed and offers enormous flexibility. Explicit joins should therefore generally be avoided in QlikView scripts. The keep functionality was designed to reduce the number of cases where explicit joins needs to be used.
Hope this helps you!!
