Example of group by and collect operator, PL-SQL Programming

Assignment Help:

Example of GROUP BY and COLLECT Operator

Example: Using GROUP BY and COLLECT to obtain C_ER2

SELECT CourseId,

CAST (

COLLECT (ROW (StudentId, Mark))

AS ROW (StudentId SID, Mark INTEGER) MULTISET)

AS ExamResult

FROM EXAM_MARK

GROUP BY CourseId

Explanation

  • ROW (StudentId, Mark) forms the row consisting of the StudentId and Mark values of the current row of EXAM_MARK, in that order. The two fields of this row are unnamed.
  • COLLECT (ROW(StudentId, Mark)) collects together as a multiset all of those rows that are derived EXAM_MARK rows having the same CourseId value. In fact it is shorthand for FUSION (ROW (StudentId, Mark) MULTISET), where FUSION is SQL's nearest counterpart of aggregate UNION. For each value of its operand, COLLECT derives the multiset containing just that value, and returns the FUSION (see next bullet) of all the multisets thus formed.
  • FUSION is aggregate multiset union (UNION ALL), not UNION per se. In general the same value (in our example, a row) might appear more than once in the result of a COLLECT invocation. Fortunately, that won't happen here because the same StudentId, Mark combination cannot appear along with the same CourseId in more than one row of EXAM_ MARK, so DISTINCT could be omitted.
  • CAST (m AS ROW (StudentId SID, Mark INTEGER) MULTISET), where m is the above COLLECT expression, names the columns of the nested table, ExamResult. Note the need to spell out the entire declared type of ExamResult, even though it differs from that of the COLLECT expression only in the names of the two columns.

Related Discussions:- Example of group by and collect operator

Map and order methods, Map and Order Methods: The values of the scalar...

Map and Order Methods: The values of the scalar datatype like CHAR or REAL have a predefined order that allows them to be compared. While, the instances of an object type has

Example of wrap operator - sql, Example of WRAP Operator - SQL The eff...

Example of WRAP Operator - SQL The effect of Example can be obtained in SQL but note that one needs to write down not only the names of the columns being wrapped but also the

Using count, Using COUNT The COUNT returns the number of elements that...

Using COUNT The COUNT returns the number of elements that a collection presently contains. For instance, when a varray projects contains 15 elements, then the following IF con

Advantages of pl/sql, Advantages of PL/SQL The PL/SQL is a high-perform...

Advantages of PL/SQL The PL/SQL is a high-performance transaction processing, completely portable language that offers the following advantages as shown: 1) Support for SQL

Between operator-comparison operators, BETWEEN Operator The operator BET...

BETWEEN Operator The operator BETWEEN, tests whether the value lies in a specified series. That means "greater than or equivalent to low value and less than or equivalent to hig

Merge two data sources to sql azure database, Project Description: I hav...

Project Description: I have two types of data sources. One that is a list in SharePoint and another that is an access desktop database. The access desktop database is fairly com

Updating objects in pl sql, Updating Objects: To change the attributes...

Updating Objects: To change the attributes of objects in an object table, you can use the UPDATE statement, as the illustration below shows: BEGIN UPDATE persons p SET p

Using the collection methods, Using the Collection Methods The collecti...

Using the Collection Methods The collection methods below help to generalize the code and make collections easier to use and also make your applications easier to maintain:

Write an anonymous block that contains a pl/sql procedure, Write an anonymo...

Write an anonymous block that contains a PL/SQL procedure. The procedure takes two input parameter: oldZip and newZip, and it updates the zipcodes table by replacing all oldZip wit

Object types and collections - performance of application, Use Object Types...

Use Object Types and Collections The Collection types and object types increase your efficiency by allowing for the realistic data modeling. The Complex real-world entities an

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd