Example of Tables within a Table - SQL
Example: Obtaining C_ER from COURSE and EXAM_MARK
SELECT CourseId, CAST (TABLE (SELECT DISTINCT StudentId, Mark FROM EXAM_MARK AS EM WHERE EM.CourseId = C.CourseId)
AS ROW (StudentId SID, Mark INTEGER) MULTISET)
AS ExamResult FROM COURSE AS C
The values for columns such as ExamResult in this example have sometimes been referred to informally as nested tables, being "tables within a table", so to speak. Unfortunately, however, they are not actually tables, but rather multisets of rows. Because of that fact, a column such as ExamResult cannot appear as an element in a FROM clause.