Grouping and ungrouping in sql, PL-SQL Programming

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Grouping and Ungrouping in SQL

Example specifying EXAM_MARK in place of COURSE in the main FROM clause.

Example: Obtaining C_ER2 from EXAM_MARK

SELECT CourseId,

CAST (

TABLE (SELECT DISTINCT StudentId, Mark

FROM EXAM_MARK AS EM2

WHERE EM1.CourseId = EM2.CourseId)

AS ROW ( StudentId SID, Mark INTEGER ) MULTISET )

AS ExamResult

FROM EXAM_MARK AS EM

Figure shows the result, named C_ER2 for convenience. It differs from the C_ER of Figure 5.3 only in the absence of a row for course C4, whose exam nobody sat.

140_Grouping and Ungrouping in SQL.png

Figure: Intermediate result C_ER2

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