The assignment operation (←) provides a convenient way to express complex queries. It allows the query to be written as a sequential program consisting of a series of assignments followed by an expression whose value is displayed as the result of the query.
Assignment must always be made to a temporary relation variable.
The result to the right of the ← is assigned to the relation variable on the left of the ←.
You may use the variable in subsequent expressions.
Example:
In this example:
1. Temp1 is assigned the result of a selection operation on Relation1 with condition1.
2. Temp2 is assigned the result of a selection operation on Relation2 with condition2.
3. Result is assigned the union of Temp1 and Temp2.
