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

Use the pls_integer datatype - performance of application, Use the PLS_INTE...

Use the PLS_INTEGER Datatype When you require to declare an integer variable, use the datatype PLS_INTEGER that is the most efficient numeric type. That is as the PLS_INTEGER

%rowcount, %ROWCOUNT When its cursor or cursor variable is opened, the...

%ROWCOUNT When its cursor or cursor variable is opened, the %ROWCOUNT is zeroed. Before the first fetch, the %ROWCOUNT yields 0. Afterward, it yields the number of rows fetche

Create a procedure to tax calculation task, Complete the following steps to...

Complete the following steps to create a procedure to calculate the tax on an order. The BB_TAX table contains the states that require taxes to be submitted for Internet sales. If

Referencing records, Referencing Records Unlike the elements in a coll...

Referencing Records Unlike the elements in a collection, that are accessed using subscripts, the fields in a record are accessed by name. To reference an individual field, you

Authorisations - privileges, Authorisations - Privileges As relational...

Authorisations - Privileges As relational theory is silent on the issue of authorisation, it offers nothing with which SQL's vast edifice in support of what it calls privilege

Package utl file in pl/sql, UTL_FILE: The Package UTL_FILE permits you...

UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,

Theory of panspermia - origin of life, THEO R Y OF PANSPERMIA - Arrh...

THEO R Y OF PANSPERMIA - Arrhenius (1908) postulated the cosmic panspermia theory that claims that organisms existed throughout the universe, and their spores, etc., could

Using aliases-declarations in sql, Using Aliases The Select-list items f...

Using Aliases The Select-list items fetched from a cursor related with the %ROWTYPE should have simple names or, if they are expressions, should have aliases. In the example bel

When are constraints checked - sql, When Are Constraints Checked Unde...

When Are Constraints Checked Under the model constraints are conceptually checked at all statement boundaries (and only at statement boundaries). By default the same is true

Oracle PL SQL, I need to write one function and one procedure to query a Or...

I need to write one function and one procedure to query a Oracle 10.1 DB using PL SQL. I have the schema and exact queries...along with work Ive started and a template to put the a

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