This lookup is slitely different from normal lookup.
The difference is
1 - the reference Link comes from database .
2 - the database record should be more than source file means ( proposnately more than min (1:100 ) proposnate required)
If these criteria matched with look up then we called that look up is sparch lookup
Sparse lookup: For each incoming row from the primary link, the SQL is fired on database at run time.
Sparse lookup can be used if the input data is smaller than the reference data.
In Sparse lookup stage, each primary records are sent to the Source and cross verified with the reference records. We use sparse lookup when the data coming have memory sufficiency and the primary records is relatively smaller than reference date we go for this sparse lookup.