- Two tables are involved:
- customer c: Refer to customer as c.
- ord o: Refer to ord as o.
- where What follows is a predicate
qualifying rows.
- c.customer_id = o.customer_id:
Connects rows of customer and ord by matching customer_id.
This is a join.
- o.ord_date between 'April 1, 2012' and 'April 30, 2012': Look for dates in April 2012.