Adventures in Machine Learning

Mastering Views in SQL: Simplifying Data Extraction and Management

Introduction to Views in SQL

As databases become more complex, it can become challenging to extract information effectively. That’s where views come in handy.

They allow you to organize data in a logical manner, making it easier to access and process. In this article, we will define and explain what views are, why they are helpful, and how to create them.

We will compare them to tables, and provide situations where views are useful. Whether you’re a beginner or an experienced SQL programmer, this article will help you understand how views work.

Definition and Function of Views

A view is a virtual table that returns the result of a SQL query. In other words, it’s a named SELECT statement that produces a result set that can be referenced as if it were a table.

Views do not store data; they extract it from one or more tables in the database. Views allow you to present the data in a way that is more meaningful and logical to the user.

For instance, imagine you have a database with several tables that contain information about Olympic games such as the event, athletes, and medals. With views, you can summarize the data and produce results such as the total number of medals won by a specific country, athlete, or event.

Views can also be used to control access to data by displaying only necessary fields to users based on their level of authorization.

Difference between Views and Tables

Tables are physical storage objects in a database that hold data. They are used to store information in a way that can be easily retrieved and analyzed.

However, unlike tables, views do not store data. Instead, they provide a virtual representation of the data extracted from one or more tables.

Views are dynamic and change as the underlying tables change. In contrast, tables remain static until new data is inserted, updated, or deleted.

Another significant difference between views and tables is data redundancy. Tables can contain duplicate data, leading to inconsistencies, which can be challenging to correct.

With views, data redundancy is minimized as they extract specific data from tables, preventing the need to store data multiple times.

Situations where Views are Helpful

There are situations where using views can significantly simplify data extraction and management. For example, views can be used to summarize information from multiple tables.

This type of view provides a concise summary of the data and eliminates the need to access individual tables. Views can also be used to reduce noise in data by presenting only necessary fields to users based on their level of authorization.

Administrators can use views to see all fields, while other users can see only specific fields that are relevant to their job.

Creating a Simple View

Now that we have an understanding of what views are and why they are helpful, let’s look at how to create a simple view.

Sample Tables

We will use two tables for our example: one for the Olympic games and the other for the medals. The Olympic games table has the following fields: id, event_name, event_time, and host_country.

The medals table has the following fields: medal_id, athlete_name, event_name, medal_type, and year.

Syntax and Creation of Views

The syntax for creating a view is as follows:

CREATE VIEW view_name

AS

SELECT column1_name, column2_name, …

FROM table1_name

JOIN table2_name

ON table1_name.column_name = table2_name.column_name

WHERE condition;

Let’s create a view that will return all the gold medalists and their events:

CREATE VIEW gold_medalists AS

SELECT medals.athlete_name, medals.event_name

FROM medals

WHERE medals.medal_type = ‘gold’;

The above code creates a view named gold_medalists that returns the name of the athlete and the event they won a gold medal in.

Using Views in SELECT Statements

Once you have created a view, you can use it in SELECT statements just like a table. For instance, to display all the gold medalists, you can use the following code:

SELECT *

FROM gold_medalists;

If you want to combine multiple views, you can use the JOIN clause.

The JOIN clause will join the views based on the columns specified.

Conclusion

Views are a powerful tool that can help manage complex data structures in a logical and organized manner. They are a virtual representation of data extracted from one or more tables that allow you to simplify data extraction, reduce noise, and control user access.

We have highlighted how to create a simple view with sample tables, and we have demonstrated how to use the view in SELECT statements. With this knowledge, you are well-equipped to start using views to simplify data management in your SQL databases.

Views with Calculated Fields

In the previous section, we discussed how to create simple views by extracting data from tables. In this section, we will discuss how to create views that display calculated fields.

We will use the example of reporting on medal counts for countries in Olympic games.

Example of Reporting on Medal Counts

In Olympic games, countries compete for medals in various events. Some countries win more medals than others, and it’s important to keep track of these medal counts.

We can create a view that calculates the medal counts for each country. Assume we have two tables: one for Olympic games and the other for medals.

The Olympic games table has the following fields: id, event_name, event_time, and host_country. The medals table has the following fields: medal_id, athlete_name, event_name, medal_type, and year.

To create a view that shows the total number of gold, silver, and bronze medals that each country has won, we can use the following SQL code:

CREATE VIEW medal_counts AS

SELECT host_country,

SUM(CASE WHEN medal_type = ‘gold’ THEN 1 ELSE 0 END) AS gold_medals,

SUM(CASE WHEN medal_type = ‘silver’ THEN 1 ELSE 0 END) AS silver_medals,

SUM(CASE WHEN medal_type = ‘bronze’ THEN 1 ELSE 0 END) AS bronze_medals

FROM olympic_games JOIN medals ON olympic_games.event_name = medals.event_name

GROUP BY host_country;

Let’s take a closer look at the SQL code.

Syntax and Creation of

Views with Calculated Fields

To create a view with calculated fields, we use the AS sub-clause to give the field a name and apply functions to it. In our example, we use the SUM function to count the number of gold, silver, and bronze medals that each country has won.

We use the JOIN clause to combine the two tables and the GROUP BY clause to group the results by host_country. This way, we get a total count of medals for each country.

Using

Views with Calculated Fields in SELECT Statements

Now that we have created a view that calculates the medal counts for each country, we can use it in SELECT statements. For instance, to display all the medal counts, you can use the following code:

SELECT * FROM medal_counts;

This will display a table showing all the countries and the number of gold, silver, and bronze medals that they have won.

Using Views Over Other Views

In this section, we will discuss how to create views based on other views. We will use the example of creating a ranking system for countries in Olympic games.

Creating a Ranking System for Countries

A ranking system for countries is based on a point system that assigns a certain number of points to gold, silver, and bronze medals. For example, a gold medal may be worth three points, a silver medal may be worth two points, and a bronze medal may be worth one point.

By summing up all the points for each country, we can create a ranking system. We can use the medal_counts view that we created earlier to create a new view that calculates the number of points each country has earned.

To create this view, we use the following SQL code:

CREATE VIEW country_points AS

SELECT host_country,

SUM(CASE WHEN medal_type = ‘gold’ THEN 3

WHEN medal_type = ‘silver’ THEN 2

WHEN medal_type = ‘bronze’ THEN 1 ELSE 0 END) AS points

FROM olympic_games JOIN medals ON olympic_games.event_name = medals.event_name

GROUP BY host_country;

The above code creates a view named country_points that returns the name of the country and the points earned.

Creation of Views Based on Other Views

We can create views based on other views to simplify queries and make them more efficient. By creating a new view that uses other views, we can avoid duplicating code and simplify our queries.

The view we created earlier, country_points, is based on the medal_counts view. By using the medal_counts view, we avoid duplicating the code for calculating medal counts.

Using Views Based on Other Views in SELECT Statements

Once we have created a view based on another view, we can use it in SELECT statements. For instance, to display the ranking of countries based on their points, we can use the following code:

SELECT host_country, points FROM country_points

ORDER BY points DESC;

This will display a table showing all the countries and their points in descending order.

Conclusion

Views with calculated fields and views based on other views are powerful tools in SQL that simplify database queries. We have shown how to create views that calculate medal counts for countries in Olympic games and how to create a ranking system for countries.

Additionally, we have demonstrated how to use views in SELECT statements and discussed the benefits of using views based on other views. With this knowledge, you can start to use views to simplify your SQL queries and improve their efficiency.

Learning More about Views

In the previous sections, we have covered the basics of views in SQL, explored situations where views are helpful, and learned how to create views with calculated fields and based on other views. In this section, we will dive deeper into views and explore their usage in INSERT, UPDATE, and DELETE statements.

Additionally, we will provide recommendations for further learning about views in SQL. View Usage in INSERT, UPDATE, and DELETE Statements

Views are often used in SELECT statements to retrieve data from the database.

However, they can also be used in INSERT, UPDATE, and DELETE statements. It’s worth noting that not all views can be used in these statements.

When creating views that might be used in INSERT, UPDATE, and DELETE statements, it’s important to ensure that the view is updatable. Updatable views are views that meet certain criteria, such as being defined on a single table, not having GROUP BY, HAVING, or DISTINCT clauses, and not having functions in the SELECT statement.

If a view meets these criteria, it can be used in INSERT, UPDATE, and DELETE statements. For instance, suppose we have a simple view named gold_medalists that shows the name of the athlete and the event they won a gold medal in.

We can use this view in an INSERT statement as follows:

INSERT INTO medals (athlete_name, event_name, medal_type, year)

SELECT athlete_name, event_name, ‘gold’, 2021

FROM gold_medalists;

The above code will insert the name of the athlete, event name, medal type, and year into the medals table for each athlete that won a gold medal in the Olympics. It’s important to note that views created with the READ ONLY option cannot be used in INSERT, UPDATE, and DELETE statements.

These views are intended for read-only purposes and do not allow changes to the data. By using the READ ONLY option, we can prevent unintentional changes to the data.

Recommendations for Further Learning

If you’re interested in learning more about views in SQL, there are several courses and resources available online. One recommendation is the SQL Views course offered by Udemy.

This course covers the basics of views in SQL, creation and usage of views with examples, and how to optimize the views for fast performance. The course material is suitable for beginners who want to learn about views and advanced users who want to improve their views usage skills.

Another recommendation is the SQL Basics course offered by Coursera. This course covers the basics of SQL, including creating views, writing common queries, and aggregating data with GROUP BY.

The course is comprehensive and well structured, making it an excellent resource for beginners who want to start learning SQL. Additionally, online tutorials and forums such as Stack Overflow can be helpful in learning about views and troubleshooting various issues.

These resources provide an opportunity to learn from experts and practitioners who have experience working with views and databases.

Conclusion

Views are an important tool in SQL that simplifies data extraction and management. In this article, we have covered the basics of views, explored situations where views are helpful, and learned about creating views with calculated fields and based on other views.

We have also explored the usage of views in INSERT, UPDATE, and DELETE statements and provided recommendations for further learning about views in SQL. With this knowledge, you can start to use views more effectively in your database queries and make data analysis more efficient.

Views are an essential component of SQL databases that simplify data extraction, management, and analysis. In this article, we have defined and explained what views are, the difference between views and tables, situations where views are useful, and how to create views with calculated fields and based on other views.

Further, we have looked into the usage of views in INSERT, UPDATE, and DELETE statements, and recommended resources for further learning about views in SQL. Overall, the main takeaway is that views can enhance data organization, access, and control, and a working knowledge of views is crucial for anyone working with SQL databases.