Mastering PostgreSQL, SELECT CASE Statement

Mastering PostgreSQL — Streamline Your Data with the CASE Statement

Data management is an integral part of successful business operations. If you rely on a relational database management system for any application, PostgreSQL is a powerful solution. In this article, we'll review PostgreSQL as well as analyze the CASE statement in PostgreSQL. We'll look at the specific value and potential applications of this statement and see how to integrate it into your code. Available as a general and simple statement, this flexible expression can be used to form any number of conditional logic queries.

What is PostgreSQL?

PostgreSQL is a relational database management system (RDBMS) with many possible applications. This open-source system has been developed over 35 years, and it's earned a strong reputation for reliability and performance. Previously known as POSTGRES, PostgreSQL enjoys broad extensibility and robust SQL compliance. It has been designed to handle various workloads, from isolated machines and single users to data warehouses and web services with many concurrent users.

PostgreSQL was the default database for macOS Server, and it's also available for Windows, Linux, FreeBSD, and OpenBSD. PostgreSQL features transactions with ACID properties: atomicity, consistency, isolation, and durability. Among other powerful features, it also benefits from automatically updatable views, materialized views, triggers, foreign keys, and stored procedures.

What is the CASE statement in PostgreSQL?

In PostgreSQL, the CASE expression is similar to the ubiquitous IF/ELSE statement used in other programming languages. It provides if-else logic to a PostgreSQL query, allowing you to bifurcate the flow of your program through binary logic or comparison. CASE is an expression, and you can use it anywhere an expression can be used. For example, you can use it with the SELECT, WHERE, GROUP BY, and HAVING clauses.

Just like IF/ELSE statements, the CASE expression goes through the listed conditions and returns a value. This value is returned when the first CASE condition is met, or when the subsequent ELSE condition is met.

  • If the initial CASE condition is true, the program will stop and return the result.
  • If this condition is not true, the value in the ELSE part of the program is returned.
  • If there is no ELSE clause or no conditions are met, the program returns NULL.

The CASE field needs a name, which can be given directly as an alias or created by the program as a default. When a column name is not specified for the CASE field, the parser uses "case" as the default column name. If you want to specify a column name, add an alias after the END keyword.

The CASE expression has two forms, and it's important to understand each one:

General CASE form

In the general syntax, each WHEN clause is a condition or Boolean expression that returns either true or false as a result.

  1. If the initial WHEN condition evaluates to true, the CASE expression returns the result following THEN. In this situation, the program does not evaluate the next expression.
  2. If the initial WHEN condition evaluates to false, the CASE expression evaluates the next condition from top to bottom until one is satisfied and evaluates to true.
  3. If all WHEN conditions evaluate to false, the CASE expression returns the result that follows ELSE. If the ELSE clause is omitted, the CASE expression returns NULL.

Simple CASE form

In the simple syntax, each WHEN clause is a value or comparative expression that compares multiple values and delivers a result.

  1. If the initial WHEN value corresponds to the CASE expression, the result following the THEN clause is returned and the program does not evaluate the next expression.
  2. If the initial WHEN does not correspond, the CASE expression evaluates the next value from top to bottom until it equates with a specific value in the THEN clause. The CASE expression returns the corresponding result.
  3. If the CASE expression does not find any exact matches between the WHEN value and the THEN result, it returns the result that follows ELSE. If the ELSE clause is omitted, the CASE expression returns NULL.

Potential uses for the PostgreSQL CASE statement

The PostgreSQL CASE statement is a basic programming construct with wide-ranging use cases. Just like the common IF/ELSE statement, it can be used whenever values need to be compared. The General CASE form is a logical expression that returns true or false, and the Simple CASE form is a comparative expression that returns one of several possibilities. Both of these constructs provide a powerful form of conditional logic.

Practical applications for the PostgreSQL CASE statement include everything from database management and commerce to research and development. This basic programming construct is particularly useful for use cases that involve long tables and complex relational databases, including inventory management, warehousing, transportation, payroll, administration, and countless other scenarios. As the world's most advanced open source relational database, PostgreSQL works with various ETL (extract, transform, and load) tools and is designed to handle all scenarios

The Panoply advantage

At Panoply, we help unlock your data to deliver key insights for better business decisions. Siloed, disparate data is difficult to access and leads to more manual tasks, higher costs, and longer time to insight. 

The Panoply cloud data platform acts as a single source of truth for all your consolidated data, connecting in just a few clicks to both your data sources and BI tool. We can also help you integrate PostgreSQL with your BI tool for better, faster visualizations.

If you want to learn more about PostgreSQL and how it can streamline your data process, book a personalized demo today.

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