Providing Results of Queries

Expressing queries in SQL is the (big) subject. Here I present just a simple example to give you the flavour of things to come in those chapters. Example is a query expressing the question, who is enrolled on course C1?

Example: A query in SQL

SELECT DISTINCT StudentId, Name

 FROM ENROLMENT

WHERE CourseId = CID ('C1')

Note carefully that Example not a command (hence the absence of a semicolon). It is just an expression, denoting a value -in this case, a table. In SQL the result of a query is always another table. Figure shows the result of Example in the usual tabular form.

                                                                   Figure: Result of query in Example

Explanation:

1. SELECT DISTINCT StudentId, Name specifies that the result of the WHERE invocation is to be projected over StudentId and Name.
2. FROM ENROLMENT specifies the table operand for the invocation of WHERE
3. WHERE CourseId = CID ('C1') specifies that just the rows for course C1 are required.