What is the difference between source qualifier and lookup?

Source Qualifier	Lookup
In source qualifier it will push all the matching records.	Where as in lookup we can restrict whether to display first value, last value or any value
In source qualifier there is no concept of cache.	Where as in lookup we concentrate on cache concept.
When both source and lookup are in same database we can use source qualifier.	When the source and lookup table exists in different database then we need to use lookup.