PL/pgSQL is a loadable procedural language for the PostgreSQL database system. It allows developers to write complex logic and functions in a more powerful and flexible language than standard SQL.
Let’s learn how to install it and use it.
What Is PL/pgSQL?
PL/pgSQL is a block-structured language that provides control structures such as loops and conditionals, as well as complex data types and other programming language features. It is particularly useful for tasks requiring complex computation or not easily accomplished with standard SQL.
Installing the PL/pgSQL Extension
Before you can use PL/pgSQL, you must install it. Here's how:
1. Connect to the PostgreSQL database where you want to install the extension. On Timescale, you can find available extensions by going to Operations > Extensions from your service overview, which will also give you installation instructions.
2. Run the following SQL command:
CREATE EXTENSION IF NOT EXISTS plpgsql;
This command installs the PL/pgSQL extension if it is not already installed.
Using the PL/pgSQL Extension
To use PL/pgSQL, you write functions in the PL/pgSQL language and then call them from your SQL queries. Here is an example of a simple PL/pgSQL function:
CREATEFUNCTION add_numbers(integer,integer)RETURNSintegerAS $$
BEGINRETURN $1+ $2;END;
$$ LANGUAGE plpgsql;
This function takes two integers as input and returns their sum. You can call this function from a SQL query like this:
Time-Series Use Cases for the PL/pgSQL Extension
PL/pgSQL is particularly useful for time-series data, where you often need to perform complex calculations over a series of data points. For example, you might use PL/pgSQL to calculate moving averages, perform time-series forecasting, or detect anomalies in your data.
Using PL/pgSQL With Timescale and Time-Series Data
If you're using Timescale for time-series data, you can use PL/pgSQL to write complex queries and calculations. For example, you might use PL/pgSQL to write a function that calculates the moving average of a time-series data set:
This function calculates the moving average of the value column in my_table, using a sliding window of size time_interval.
Below is an example test setup for the moving_average function:
1. First, we'll create a dummy table my_table with some sample data.
2. Then, we'll call your moving_average function with a specified time interval.
3. Lastly, we'll query the result to observe the computed moving averages.
-- 1. Setup: Create the my_table and insert some sample dataDROPTABLEIFEXISTS my_table;CREATETABLE my_table (time TIMESTAMPTZ,valueDOUBLEPRECISION);
-- Let's insert some sample data. Imagine this data represents some sensor readings taken every 10 minutes.INSERTINTO my_table (time,value)VALUES('2023-08-21 08:00:00',5),('2023-08-21 08:10:00',6),('2023-08-21 08:20:00',5.5),('2023-08-21 08:30:00',6.5),('2023-08-21 08:40:00',7),('2023-08-21 08:50:00',6.5);
-- 2. Test: Call the moving_average function for a 30-minute time interval.-- This will average the values over each 30-minute period.SELECT*FROM moving_average('30 minutes'::INTERVAL)GROUPBY1,2ORDERBY1;-- The result should be:-- '2023-08-21 08:00:00', 5.5 (Average of 5, 6, 5.5)-- '2023-08-21 08:30:00', 6.67 (Average of 6.5, 7, 6.5)
The test setup above clearly shows how to utilize the moving_average function. You'll be able to observe the computed moving averages for the given sample data and the specified time interval.