Join Relationships
The simple joins illustrated in the two preceding examples depend on equal values in the join columns. This type of join is called an equijoin. Other types of relationships can be specified in a join. For example, the following query lists salespersons who have met or exceeded their sales quota:
SELECT s.name, s.sales_ytd
FROM sales s, quotas q
WHERE s.empnum = d.empnum AND
s.sales_ytd >= d.quota;