Extracting Values from JSON in PostgreSQL: A Simple Solution

Learn how to efficiently extract values from JSON columns in PostgreSQL, with a focus on currency exchange rates, using simple SQL queries.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Extract value from JSON that matches a column value

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Extracting Values from JSON in PostgreSQL: A Simple Solution

Working with JSON data in SQL can sometimes be challenging, especially when trying to extract specific values based on different conditions. A common scenario arises when dealing with exchange rates, where one might need to extract values from a JSON column that aligns with certain criteria. In this guide, we will explore an efficient solution to help you extract values from JSON in PostgreSQL without resorting to long and cumbersome CASE statements. Let’s dive in!

The Problem

Imagine you have two tables in your PostgreSQL database. One table holds exchange rates for various currencies, formatted in JSON, while the second table keeps track of currency sales along with the corresponding sale dates. Here’s a brief overview of the tables:

Table 1: Exchange Rates

idrates_valuesrate_date1{"AED":2.835349,"AFN":67.743417,...}1-1-20222{"AED":2.485349,"AFN":66.843814}2-2-2022Table 2: Currency Sales

currencycostdate_of_saleAED1501-1-2022AFN2502-2-2022EUR562-2-2022The goal is to join these two tables on the date and extract the corresponding exchange rate for each currency from the rates_values column based on the currency column in the second table.

The Solution

To achieve this, you can use a simple SQL expression that leverages the JSONB capabilities of PostgreSQL. Here's how:

Step-by-step Explanation

Join the Tables: Use a SQL JOIN to combine the two tables based on the sale date. This will match sales with the corresponding rates.

Extract Values: Instead of writing a lengthy CASE...WHEN statement, you can directly access the JSON values using the column name as a key.

Cast to Float: Since the extracted JSON values need to be numeric, you can cast them to float.

SQL Query Example

Here’s a sample query that illustrates these steps:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Query

::float: Converts the extracted value to float for numerical operations if needed.

Conclusion

By using the JSON operators provided by PostgreSQL, you can efficiently extract specific values without the need for complex conditional logic. This not only simplifies your SQL queries but also improves performance.

Implementing this solution will significantly streamline your data extraction process. So next time you are faced with JSON values in your SQL queries, remember that there's a simpler way to get the information you need!

If you have further questions or need assistance with your PostgreSQL queries, feel free to reach out!