Processing Model and Basic Syntax video lecture

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Из курса от партнера University of Colorado System

Relational Database Support for Data Warehouses

407 оценки

University of Colorado System

Relational Database Support for Data Warehouses

407 оценки

Курс 3 из 5 — Specialization Data Warehousing for Business Intelligence

Relational Database Support for Data Warehouses is the third course in the Data Warehousing for Business Intelligence specialization. In this course, you'll use analytical elements of SQL for answering business intelligence questions. You'll learn features of relational database management systems for managing summary data commonly used in business intelligence reporting. Because of the importance and difficulty of managing implementations of data warehouses, we'll also delve into storage architectures, scalable parallel processing, data governance, and big data impacts.

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SQL Analytic Functions

After your experience using the SQL subtotal operators, you are ready to learn another important SQL extension for business intelligence applications. In module 3, you will learn about an extended processing model for SQL analytic functions that support common analysis in business intelligence applications. You’ll apply what you’ve learned in practice and graded problems using Oracle SQL for problems involving qualitative ranking of business units, window comparisons showing relationships of business units over time, and quantitative contributions showing performance thresholds and contributions of individual business units to a whole business. Because analytic functions are part of the SQL standard, your learning will apply to other enterprise DBMSs. At the end of this module, you will have solid background to write queries using the SQL analytic functions as a data warehouse analyst.

Processing Model and Basic Syntax video lecture9:10

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Michael Mannino
Associate Professor
Business School, University of Colorado Denver

Welcome to Lesson 1 of Module 3 on the Oracle SQL Analytic Functions.

An appropriate alternative title is, Fun with Analytic Functions.

I'm gonna start with an important conceptual question

that I want you to think about throughout this lesson.

What is a fundamental different between the SQL subtotal operators and

analytic functions?

Module three continues the detailed coverage from module two

with ungraded problems and a graded assignment.

Lesson one introduces Oracle SQL analytic functions with coverage of motivation,

processing extensions, basic syntax, and examples.

Although the coverage in this module is specific to Oracle SQL,

other EnterpriseDB [INAUDIBLE] provide similar capabilities.

You have three learning objectives in this lesson.

You should understand the processing extension for

analytic functions, especially as the processing relates to the GROUP BY clause.

Your most goal is to write select statements using the basic syntax for

analytic functions.

As a reflective goal, you should think about the importance

of analytic function extensions for the SQL SELECT statement.

Before getting into the details of analytic functions,

let's consider the motivation for extensions to the SQL select statement.

Business intelligence applications, typically involve analysis,

that combines data retrieval and computations.

Here are common types of analysis.

Top and worst performers providing qualitative ranking

of business units such as store sales and agent commissions.

Trends identifying changes between time periods,

often involving summary calculations on moving windows, such as moving averages.

Quantitative contributions showing the top or

bottom percentage threshold, such as the top 10% of stores by sales.

In addition, contributions to a whole can be important

such as sales agent's commissions is a part of total commissions.

Organizations found the SQL select statement

inadequate to support standard business intelligence applications.

Applications required a complex skill set involving data retrieval,

procedural coding and external tool usage.

Organizations experience difficulties

to find individuals possessing the necessary skill set.

Productivity was poor for developing business intelligence applications

with complex select statements and procedural coding often required.

Performance was slow, with SQL compilers often developing poorly performing plans

for complex select statements.

In addition, complex calculations were typically done outside of SQL statements,

so optimizing SQL compilers could not optimize both data retrieval and

computations.

To overcome these deficiencies the select statement needed a major extension for

both processing and specification.

The processing extension makes the analytic function extension more complex

than the subtotal operator extension covered in module two.

The key to understanding analytic function processing

is the new step after GROUP BY processing.

As you will see, the appearance of analytic functions in a select statement

seems to conflict with the evaluation order.

Analytic function processing occurs after row and group processing so

the calculations can be performed and grouped by results.

Many of the examples use grouping and analytic function processing because data

warehouse retrievals often combine joins and grouping on dimension and fact tables.

Analytic function processing involves organizing results into partitions,

evaluate functions over partitions, and then ordering the partitions.

Analytic function processing involves ordering as criteria

to evaluate a function, rather than ordering in the final result,

another confusing part of analytic functions.

Before examining complete select statements,

let's focus just on the basic syntax for analytic functions.

You place analytic functions in the select list.

Similar to the placement of other result columns.

Syntactically, analytic functions are by an analytic function

with an optional list of columns in the over keyboard with an ordering.

The ordering indicates a criteria for

function evaluation, not a final ordering of results.

To demonstrate the syntax, let's look at two examples with a rank function.

The rank function does not use a column list, so

the empty parentheses is required.

In the first example, ranking is computed on the item priced column.

The AS keyword renames the computed rank column.

In the second example, ranking occurs in the sum of sales dollar column.

The aggregate function sum indicates that a GROUP BY clause is necessary

in the complete select statement as you will see.

Examples in module three use the store sales tables.

Module one cover the details about the scheme and design.

Module two use the store sales tables in each lesson.

So you should be familiar with the tables.

The oracle diagram is repeated in this lesson for convenience.

Example one rank signs by unit price.

In the statement you should note the RANK function with the empty parentheses.

The OVER keyword, in the order by specification inside the OVER clause.

The ORDER BY clause indicates that rank is determined by a sending order of

ItemUnitPrice.

Sample rows indicate the values of the RANK function.

With the smallest unit price, 12, receiving the top rank, one.

I will now execute this statement using the Oracle SQL Developer.

The result contains ten rows with four columns in each row.

Each row in the SS item table appears in one result row.

Example two, ranks customers by descending some of dollar sales.

Because of the requirement to rank using the sum function,

a GROUP BY clause is required.

The order by specification in the over clause indicates that customers are ranked

using the sum function on the sales dollar column in descending order.

Thus, the first result row with a largest sum of sales obtains a top ranking of one.

I will now execute this statement using the Oracle SQL Developer.

The result contains nine rows, with three columns in each row.

Note that the GROUP BY clause generates one customer per group,

and then calculates the sum of dollar sales for each group of customers.

You should now be ready to write select statements for some additional problems.

In example three,

you should rank item brands in descending order on average dollar sales in 2010 and

2011, showing the item brand, average dollar sales, and rank and the result.

In example four you should extend example three to only include item brands

with more than ten sales and show the number of sales in a result.

You can find the solutions in a module three document.

This lesson introduced Analytic Functions.

A substantial extension to the SQL select statement in both syntax and processing.

Analytic functions support answers to common business intelligence questions,

involving ranking trends in quantitative contributions.

You learned about the evaluation order for

analytic functions in a syntax using the OVER and ORDER BY keywords.

You were encouraged to write select statements for

the practice problems to apply the details of the lesson.

In answer to the opening question, analytical functions evolve a more

fundamental change to the select statement than a subtotal operators.

Both subtotal operators and the analytic functions involve syntax changes.

Analytic functions also involve an extension of the evaluation order for

the select statement.

To become skilled with query formulation using the analytic functions

you must understanding the evaluation order,

especially the evaluation of analytic functions after group by processing and

ordering is a criteria in many analytic functions such as rank.

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