intro
By employing user-defined functions and operators, PostgreSQL provides database users and administrators with custom functionalities and data types required for use in specific cases and enhancement of the maintainability of code.
Preface
Are you looking for ways to efficiently extend the functionality of PostgreSQL and optimize its performance for specific use cases? User-defined functions and operators are what you need. With user-defined functions, you can create custom functionality that meets your specific needs and simplifies complex queries. User-defined operators, on the other hand, present more fluidity when working with custom data types.
In this guide, we will explore the power of user-defined functions and operators in PostgreSQL, their syntax and usage, and provide examples of how they can help you take your SQL game up the roof. Let’s dive into PostgreSQL and learn how to suit it to your specific needs better.
What are User-Defined Functions in PostgreSQL?
Wondering what user-defined functions in Postgres are? In PostgreSQL, user-defined functions, or UDFs, are deliberately designated functions created by users to perform a specific task. These functions are not built into the database management system. User-defined functions in PostgreSQL can be written in a variety of programming languages, including SQL, Java, PL/pgSQL, Perl, C, and Python.
They have many benefits when it comes to database optimization and performance. Some key benefits include:
Creating User-Defined Functions in PostgreSQL
User-defined functions in PostgreSQL are created with the “CREATE FUNCTION” command using a PostgreSQL client such as Postgres Shell (PSQL) or the graphical user interface (GUI) provided by pgAdmin or SQL clients. This implies a function can be created in two ways, either with the use of PostgreSQL code/PSQL or via PgAdmin GUI. We’re going to explore both methods, however, it is important to note that the syntax varies depending on the programming language used to write the function.
Creating User-Defined Functions using the PostgreSQL Shell (PSQL)
This is the general syntax for creating a basic user-defined function in PostgreSQL using PL/pgSQL:
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CREATE[OR REPLACE]FUNCTION function_name (arg_1 datatype,arg_2 datatype)
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RETURNS return_datatype AS $variable_name$
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DECLARE
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-- Declare any local variables here
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BEGIN
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-- Function logic goes here
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RETURN {variable_name|value}
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END;$$
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LANGUAGE plpgsql;
As you can see, we have a general syntax that is used to create a user-defined function in Postgres. Now, let us take a look at the parameters in the syntax.
The parameters above are the general makeup constituents of a User-defined Function. Next, let us dive deep into how UDFs are executed.
How to Run a User-Defined Function in PostgreSQL using the PSQL
To run a user-defined function, you’ll need to create the function using the CREATE FUNCTION statement, specifying the function name, input parameters, return type, and the function body. Now, after creating the function, we will go on to execute it.
For example, let’s take a look at a simple user-defined function here:
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CREATE OR REPLACE FUNCTION ADD_NUMBERS(x1 integer, x2 integer)
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RETURNS integer AS $total$
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BEGIN
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RETURN x1 + x2;
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END; $total$
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LANGUAGE plpgsql;
In the query above, we create a function that adds two integers together and returns their sum as an integer. Before we can run a user-defined function in the PSQL, we’ll first need to connect to our Postgres database by running the command below in our terminal:
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Psql -U postgres
Now, let us input the function in the terminal and create the function by ending it with a CREATE FUNCTION command as shown below:
Great! We have successfully created the function in the schema of our database. To know if the function has been created, let us run the command below in the terminal of our computer:
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\df public.*
This command lists all functions in the public schema.
Once we have successfully created the function, it is time to test the function by running or executing it. We can do so by issuing a SELECT query as SELECT ADD_NUMBERS (1,2); in the terminal. This will call the ADD_NUMBERS function with arguments 1 and 2, and return the result 3 as shown below:
This same function we have created in the PostgreSQL Shell can be created in pgAdmin. Let us dive into this in the next section.
Creating User-Defined Functions using pgAdmin
In this section, we’re going to establish the process flow on how to create user-defined functions in PostgreSQL using the pgAdmin program using a tool like DbVisualizer.
Below are the steps you can follow to create the user-defined function.
Step 1: On the left pane of the DbVisualizer window, navigate to PostgreSQL Connection ->Databases ->Postgres-> Schema-> public-> Functions as shown below:
Step 2: Select the Functions node and open the Create Function dialog from the right-click menu.
Step 3: Next, specify the function, direction, name, and type parameters.
Step 4: The details of the dialog depend on the database, but typically you need to:
You can use the other buttons to the right of the parameter list to remove and move a parameter. For example, using the ADD_NUMBERS function we used earlier, this is how our dialog is going to appear:
Step 5: Now, select the Functions node and click on ‘Refresh Objects Tree’ from the right-click menu and you’ll see that the ADD_NUMBERS function has been created.
Now, the ADD_NUMBERS function has successfully been created. The next thing on board is to execute or run the function. In the next section, we’re going to look at how to run user-defined functions, this time around, in pgAdmin.
How to Run a User-Defined Function using PgAdmin
Just as we ran the UDF earlier in the PostgreSQL Shell, we can do the same execution in the PgAdmin program to verify the output. To do this, let’s
Step 1: Open the code editor or SQL commander of DbVisualizer and write our query as shown below:
Step 2: The query can be executed by highlighting the code and selecting Execute from the right-click menu. This will call the ADD_NUMBERS function with arguments 1 and 2, and return the result 3 as shown below:
The successful return of the value 3 verifies the output of the function.
Let us dive into the next chapter of the blog which focuses on user-defined operators in PostgreSQL.
What are PostgreSQL User-Defined Operators?
PostgreSQL user-defined operators, or UDOs, are custom operators created by database developers to be used in performing operations that are not easily expressible by the default operators of a programming language. These operators can be defined for both default and custom or user-defined data types in PostgreSQL, making it a powerful medium for broadening the functionality range of PostgreSQL. In many programming languages, operators have predefined meanings by default. However, some allow users to define their operators with custom behavior.
For example, the + and - operators, for instance, can be overloaded in a language like C++ to work with models of your classes, enabling you to define unique behavior for those operators when dealing with your class models. Now that we have a fair idea of what UDOs are, let us dive into the process of creating them.
Creating PostgreSQL User-Defined Operators
Just as user-defined functions in PostgreSQL are created with the CREATE FUNCTION command, user-defined operators are created with the CREATE OPERATOR command using a PostgreSQL client such as Postgres Shell (PSQL) or pgAdmin and now, we’re going to explore both methods.
Creating User-Defined Operators using PostgreSQL Shell (PSQL)
To create a user-defined operator in PostgreSQL, you can use the following general syntax:
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CREATE OPERATOR operator_name (
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LEFTARG data_type,
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RIGHTARG data_type,
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PROCEDURE function_name
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);
As you can see, we have a basic syntax that is used to create a user-defined operator in Postgres. Now, let us take a look at the parameters in the syntax.
The parameters above are the general makeup constituents of a user-defined operator.
Next, let us dive deep into how a UDO is executed. But one thing worth noting is that operators provide a convenient, easy-to-read syntax for performing a specific operation, but behind the scenes, it's just calling a function like any other method or function in the language. This implies you must always first create the underlying function before you can create the operator.
How to Run a User-Defined Operator using PostgreSQL Shell
For an example illustrating how to run UDOs in the PostgreSQL Shell, let us consider creating an operator called ||| that concatenates two strings with a space in between as shown below:
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CREATE OPERATOR ||| (
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LEFTARG = text,
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RIGHTARG = text,
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PROCEDURE = concat_space
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);
In the query above, we're specifying that the operator takes two arguments of the data type text and uses a custom function called concat_space to concatenate the strings with a space in between. Before we can run a user-defined operator in the PSQL, we’ll first need to connect to our Postgres database by running the command below in our terminal:
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Psql -U postgres
To create the operator, we’ll first have to create the underlying function by writing the following command in the terminal as shown below:
Once the underlying function has been created, we can now proceed with creating the operator that uses it in the PSQL as shown below:
Great! We have successfully created the operator in the public schema of our database. To know if the operator has been created, let us run the command below in the terminal of our computer:
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\do public.*
This command lists all operators in the database schema.
We can now use the operator we have created in SQL queries like this SELECT 'Hello' ||| 'Doe' AS greeting; and this should return the string Hello Doe.
Just as we have created and executed a user-defined operator in the PSQL, we can do the same thing using the pgAdmin. Let us dive into this second alternative in the following section.
Creating a User-Defined Function using PgAdmin
Now, we’re going to establish the process flow on how to create a user-defined operator in PostgreSQL using the pgAdmin program. Below are the steps you can follow to create the user-defined function.
Step 1: On the left pane of the DbVisualizer window, navigate to PostgreSQL Connection ->Databases ->Postgres-> Schema-> public-> Operators as shown below in DbVisualizer:
Step 2: Select the Operators node and click the Refresh Objects Tree option from the right-click menu.
Step 3: After refreshing the objects tree, you’ll realize that the operator we created using the PSQL has reflected in the Operators node in DbVisualizer as shown below:
You might be probably asking yourself why creating a UDO is different as compared to the UDF which was created separately in the pgAdmin. The reason for the difference in behavior between UDFs and UDOs is due to the different requirements for creating and using these database objects. UDFs can be created directly in the database or using SQL scripts, while UDOs require a custom function to define their behavior and must be created directly in the database before they can be used.
How to Run a User-Defined Operator using PgAdmin
Just as we executed the UDO earlier in the PostgreSQL Shell, we can do the same execution in the pgAdmin program to verify the output. To do this, we will perform a couple of steps:
Step 1: Open the code editor or SQL commander of DbVisualizer and write our query as shown below:
Step 2: Execute the query by highlighting the code and selecting Execute from the right-click menu. This will call the ‘ concat_space’function that was specified when the ‘|||’ operator was created as shown below:
The End! Creating user-defined functions and operators in PostgreSQL has never been easier!
Conclusion
In this article, you understood what user-defined functions and operators in PostgreSQL are. Specifically, you learned that with PostgreSQL, users can create custom functions and operators that meet their specific needs and see how to create and run them.
You also saw that creating and executing UDFs and UDOs is a task that requires a complete database client with full PostgreSQL support, such as DbVisualizer. With such an advanced tool, you can write optimized queries, and take your database management to the next level. Make sure to grab a free trial of DbVisualizer here!
FAQ
Can user-defined functions and operators be shared between databases in Postgres?
Yes, user-defined functions and operators can be shared between databases in Postgres. This can be done by creating the function or operator in a schema that is shared between databases, such as the "public" schema.
Can PostgreSQL user-defined functions and operators be used in indexes?
Yes, user-defined functions and operators can be used in indexes in Postgres. This can be useful for improving query performance when working with large datasets. However, it's important to note that not all UDFs and UDOs can be used in indexes, and there are restrictions on how they can be used.
How can you debug a PostgreSQL user-defined function?
Debugging user-defined functions in Postgres can be done using the RAISE NOTICE statement. This statement allows you to print debugging messages to the server log or the client application. You can use RAISE NOTICE to print the values of input parameters or intermediate results so that you can better decipher the behavior of the function and identify any errors or unexpected behavior. Additionally, some development environments and tools, such as pgAdmin, may provide built-in debugging features for UDFs.
How can you create PostgreSQL user-defined operators that work with arrays or other complex data types?
Creating user-defined operators that work with arrays or other complex data types in Postgres requires defining custom functions that can operate on those data types. For example, if you want to create an operator that concatenates two arrays, you would need to create a custom function that takes two arrays as input and returns a concatenated array. Once the function is defined, you can create the operator using the CREATE OPERATOR statement, specifying the function as the operator's implementation.
