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

I want database development with analysis tools, Project Description: I ...

Project Description: I want a database for large governmental and private data sets on one country that will be easily extended to other countries in the future. Also, the datab

Pl/sql expressions , Pl/SQL Expressions The Expressions are constructed...

Pl/SQL Expressions The Expressions are constructed by using the operands and operators. An operand is a constant, literal, variable, or function call which contributes a value

Sequential control - pl/sql, Sequential Control Dissimilar to the IF and ...

Sequential Control Dissimilar to the IF and LOOP statements, the GOTO and NULL statements are not important to the PL/SQL programming. The configuration of PL/SQL is such that th

Write sql code that will create the writes table, Question: Consider th...

Question: Consider the following relations (primary keys are underlined): AUTHOR (ANo, aname, address, speciality) PUBLISHER (PNo, pname, Location) BOOK (BNo, Title, ISBN,

I need sql to infopath data connection, I need SQL to infopath data connect...

I need SQL to infopath data connection Project Description: Want data retrieval connection from SQL to SharePoint infopath Skills required are Sharepoint, SQL

Scope and visibility- pl/sql, Scope and Visibility The References to an ...

Scope and Visibility The References to an identifier are resolved according to its visibility and scope. The scope of an identifier is that area of a program unit (subprogram, b

Why use cursor variables, Why Use Cursor Variables ? Primarily, you use...

Why Use Cursor Variables ? Primarily, you use the cursor variables to pass the query result sets between the PL/SQL stored subprograms and different clients. Neither PL/SQL nor

Biconditional - sql, Biconditional - SQL The biconditional p ↔ q can b...

Biconditional - SQL The biconditional p ↔ q can be expressed in Tutorial D by p = q and the same is true of SQL. The question then arises as to whether, in SQL, p = q is equiv

Creating and destroying base tables, Creating and Destroying Base Tables: ...

Creating and Destroying Base Tables: Example shows an SQL command to create the base table counterpart of the ENROLMENT variable Example  Creating a base table. CREATE T

PROCEDURE, Create a procedure named DDPROJ_SP that retrieves project inform...

Create a procedure named DDPROJ_SP that retrieves project information for a specific project based on a project ID. The procedure should have two parameters: one to accept a projec

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