## Introduction to SQL Analytical Functions

SQL analytical functions are vital tools for business intelligence (BI) and data warehousing (DWH) professionals who work with vast amounts of data. These functions offer powerful and efficient ways of analyzing data, identifying patterns, and deriving actionable insights.

In this article, we will explore the importance and history of SQL analytical functions and examine some of the basic processes involved in using SQL to partition, order, and analyze data.

## History of using SQL in BI

The use of SQL in BI applications can be traced back to the late 1980s and early 1990s, when relational database systems were developed. Prior to the introduction of SQL, BI professionals used programming languages like COBOL and FORTRAN to extract data from mainframe systems.

However, this method was complex, time-consuming, and not very efficient. With the invention of SQL, BI professionals could easily extract data from relational database systems, which was a vast improvement over earlier methods.

## Problems with using standard SQL in BI

Despite the benefits of using SQL in BI, there were some limitations that hindered data analysts from processing and analyzing large amounts of data. For instance, standard SQL lacked built-in functions for ranking, offsetting, and aggregating data, which made it challenging for BI professionals to perform complex analysis.

Additionally, standard SQL did not offer a straightforward way of partitioning data, which meant that analysts had to use workarounds to retrieve data in the desired format.

## Need for SQL extensions for processing and specification

To address the shortcomings of standard SQL, various SQL extensions were developed, each with unique features and capabilities. These extensions included SQL Server Analysis Services (SSAS), Oracle Business Intelligence (OBI), Sybase IQ, and others.

These extensions offered powerful query optimization features, improved data processing capabilities, and support for advanced analytics functions. As a result, BI professionals could now perform complex analyses, generate reports, and extract insights from massive amounts of data quickly and easily.

## Common computations in BI applications

BI professionals perform various computations to extract insights from the data they analyze. Some of the common computations include ranking, offsetting, aggregation, and partitioning.

Ranking is the process of assigning numerical values to data based on certain criteria, such as volume, frequency, or time. Offset functions enable analysts to specify a range of values to retrieve from a data set.

Aggregation functions allow analysts to summarize data by performing calculations on groups of data. Finally, partitioning is a technique used to retrieve subsets of data based on specific criteria and separate them from the rest of the data set.

### Importance of SQL analytical functions for BI/DWH professionals

- Improved data processing capabilities: SQL analytical functions allow BI professionals to process massive amounts of data quickly and efficiently.
- Advanced analytics functions: SQL analytical functions offer advanced analytics capabilities, such as data mining, forecasting, and predictive modeling.
- Better data visualization: SQL analytical functions allow BI professionals to create visualizations that make it easier to understand complex data.
- Improved decision-making: SQL analytical functions enable BI professionals to generate actionable insights and drive better decision-making.

### Basic processes involved in using SQL to partition, order, and analyze data

#### 1. Partitioning

Partitioning is a technique used to retrieve subsets of data based on certain criteria.

To partition a data set, BI professionals use the PARTITION BY clause in their SQL statements. This clause allows analysts to divide a data set into partitions based on specific criteria, such as date, location, or product.

#### 2. Ordering

Ordering is the process of sorting data in ascending or descending order.

To order a data set, BI professionals use the ORDER BY clause in their SQL statements. This clause allows analysts to sort data based on specific criteria, such as time, value, or location.

#### 3. Analyzing

To analyze data, BI professionals use various SQL analytical functions such as SUM, AVG, MAX, MIN, and COUNT.

These functions allow analysts to perform calculations and extract insights from data sets quickly and easily.

## Conclusion

In conclusion, SQL analytical functions are essential tools for BI and DWH professionals who work with large amounts of data. SQL extensions such as SSAS, OBI, and Sybase IQ have helped to address the shortcomings of standard SQL, enabling BI professionals to perform more complex analysis and derive actionable insights from massive data sets.

By mastering the basic processes involved in using SQL to partition, order, and analyze data, BI professionals can use SQL analytical functions to generate insights that lead to better decision-making.

## SQL Analytical Functions: The Basics

SQL analytical functions are powerful tools that allow BI and DWH professionals to perform complex data analyses with ease.

These functions, also known as window functions, operate on a set of rows and generate results based on groups defined by partitions or window specifications. In this article, we will explore the definition and purpose of analytical functions, the order of processing analytical functions in SQL, and the syntax of analytical functions.

### Definition and purpose of analytical functions

Analytical functions are SQL functions that operate on a set of rows and return a single aggregate result for each row. These functions enable BI professionals to perform advanced calculations and analysis on large data sets without having to use complex queries.

Analytical functions differ from aggregate functions in that they operate on a subset of data rather than the entire data set. The primary purpose of analytical functions is to extract more information and insights from data sets.

### Order of processing analytical functions in SQL

SQL processes analytical functions in a specific order. First, it processes the SELECT and FROM clauses.

Then, it checks for the presence of analytical functions and processes them before any non-aggregate functions. Finally, it processes GROUP BY and HAVING clauses.

### Syntax of analytical functions

The syntax for analytical functions is as follows:

`function (x) OVER (window_spec)`

In the above syntax, `function`

is the analytical function like SUM, AVG, MAX, MIN, RANK, DENSE_RANK, and NTILE. `x`

is the value that the function will operate on.

The `OVER`

clause defines the window or partition in the result set over which the analytical function will calculate.

## Ranking Functions

Ranking functions are a type of analytical function that allow BI professionals to rank rows within a data set. These functions assign a rank to each row based on a specific criterion and are useful for identifying outliers or anomalies.

There are several types of ranking functions, including the RANK function, the DENSE_RANK function, the NTILE function, and the ROW NUMBER function.

### RANK function and its syntax

The RANK function assigns a unique rank to each row within a set, based on a specific criterion. In the event of a tie, the RANK function assigns the same rank to all the rows with equal values.

The syntax for the RANK function is as follows:

`RANK () OVER (ORDER BY x)`

In the above syntax, `x`

is the column that is being ranked.

### DENSE RANK function and its differences from RANK

The DENSE RANK function assigns a unique rank to each row within a set, based on a specific criterion. In the event of a tie, the DENSE RANK function assigns the same rank to all the rows with equal values, like the RANK function.

However, unlike the RANK function, the DENSE RANK function does not leave any gaps in the ranks when there are ties. The syntax for the DENSE RANK function is as follows:

`DENSE RANK () OVER (ORDER BY x)`

### NTILE function and its purpose

The NTILE function divides a set of rows into a specified number of groups, based on a specific criterion, such as value, frequency, or volume.

Each row is assigned to a group based on its value, with each group containing an equal number of rows as closely as possible. The syntax for the NTILE function is as follows:

`NTILE(x) OVER (ORDER BY y)`

In the above syntax, `x`

is the number of groups to divide the data into, and `y`

is the column to order the data by.

### ROW NUMBER function and its differences from RANK and DENSE RANK

The ROW NUMBER function assigns consecutive numbers to each row in a result set, starting from 1. Unlike the RANK and DENSE RANK functions, ROW NUMBER does not skip any numbers if there are ties.

The ROW NUMBER function is useful for pagination and identifying specific rows in a data set. The syntax for ROW NUMBER is as follows:

`ROW NUMBER () OVER (ORDER BY x)`

In the above syntax, `x`

is the column that is being ordered.

## Conclusion

In conclusion, SQL analytical functions, and ranking functions, in particular, are powerful tools that enable BI and DWH professionals to perform complex data analysis with ease. They allow for the extraction of more information and insights from data sets, aiding better decision-making.

The order by which SQL processes analytical functions, and the syntax of these functions are straightforward and easy to follow. RANK, DENSE RANK, NTILE, and ROW NUMBER are all important ranking functions that each have specific use cases in data analysis.

With a clear understanding of these functions and their applications, BI professionals can generate more informed insights and make better decisions from their data.

## Positional Analytical Functions

Positional analytical functions are another type of analytical function that operate on a set of rows and return a single result for each row. Rather than ranking rows, they enable BI professionals to evaluate values that are a certain number of rows ahead or behind a given row, based on a specific criterion.

The two types of positional analytical functions are the LEAD function and the LAG function.

### LEAD function and its syntax

The LEAD function retrieves data from the next row within a given range, based on a specific criterion, such as value, date or time. The first argument of the LEAD function specifies the column to retrieve data from, while the second argument specifies the number of rows to retrieve data from.

By default, the third argument is the subsequent row of the current row that the function is evaluated. The syntax for the LEAD function is:

`LEAD (column_name, offset, default_value) OVER (ORDER BY ...)`

In the above syntax, `column_name`

is the name of the column to retrieve data from, `offset`

is the number of rows forward from the current row to retrieve data, `default_value`

is the value to return if there are no rows to retrieve, and ORDER BY specifies the column to order by.

### LAG function and its syntax

The LAG function is the opposite of the LEAD function, as it retrieves the value of a given column in the previous row, based on a specific criterion. The first argument of the LAG function specifies the column to retrieve data from, while the second argument specifies the number of rows to retrieve data from.

By default, the third argument is the previous row of the current row that the function is evaluated. The syntax for the LAG function is:

`LAG (column_name, offset, default_value) OVER (ORDER BY ...)`

In the above syntax, `column_name`

is the name of the column to retrieve data from, `offset`

is the number of rows back from the current row to retrieve data, `default_value`

is the value to return if there are no rows to retrieve, and ORDER BY specifies the column to order by.

## Summary Functions

Summary functions are aggregate functions that perform calculations on a set of values and return a single result. There are several types of summary functions, including SUM, AVG, MAX, MIN, and COUNT.

### SUM function

The SUM function is an aggregate function that calculates the sum of a set of values. The syntax for the SUM function is:

`SUM (column_name)`

In the above syntax, `column_name`

is the name of the column to sum. Summary functions are useful for gaining insights into large data sets quickly and easily.

They often form the basis of broader BI queries, such as reports or dashboards, and are instrumental in driving data-driven decision-making. By performing calculations quickly and efficiently, summary functions enable BI professionals to analyze large amounts of data with ease.

## Conclusion

In conclusion, positional analytical functions and summary functions are important tools that enable BI and DWH professionals to perform advanced calculations and analysis on large data sets. The LEAD and the LAG functions, in particular, are useful for retrieving data from the next or previous rows based on specific criteria, while summary functions like the SUM function enable BI professionals to extract information from a group of rows quickly and efficiently.

By mastering these functions, BI and DWH professionals can significantly improve their ability to work with vast amounts of data and generate insights that lead to better decision-making. SQL analytical functions are powerful tools that enable BI and DWH professionals to perform complex data analysis and gain insights that aid better decision-making.

These functions allow for the extraction of more information and insights from data sets and facilitate fast and efficient data processing. Ranking functions like RANK, DENSE RANK, NTILE, and ROW NUMBER are instrumental in identifying outliers or anomalies, while LEAD and LAG functions enable retrieval of data from a specified range ahead or behind a given row.

Summary functions such as SUM, AVG, MAX, MIN, and COUNT make it easier to generate insights quickly and efficiently. A clear understanding of these functions and their applications enables BI professionals to generate informed insights and make better decisions from their data.