Examples of PostgreSQL Stored Procedures: The Ultimate Guide

On a broader level, PostgreSQL supports several procedural languages that help sustain data models that repeat previous values. PostgreSQL Stored Procedures support procedural operations, which are helpful while building powerful database apps — they increase their performance, productivity, and scalability. Like UDFs, stored procedures are a sequence of SQL statements available to apps that access an RDBMS.

In short, developing custom functions becomes easier using the PostgreSQL Stored Procedures. Moreover, once created, you can deploy stored procedures in any app based on your requirements. So, with this ultimate guide, you will learn about Stored Procedures in PostgreSQL in detail. And, through some workflow examples, you will also be able to apply the learnings in real-life situations, too. Let’s begin.

How to CREATE OR REPLACE PostgreSQL Stored Procedures?

In PostgreSQL, CREATE OR REPLACE PROCEDURE exists to create a new procedure or deploy a new definition in place of an existing one. To be able to CREATE OR REPLACE PROCEDURE, for a user in PostgreSQL, having a USAGE privilege on the language is a prerequisite.

The syntax to CREATE or REPLACE PostgreSQL Stored Procedures is given below:

CREATE [ OR REPLACE ] PROCEDURE
    name ( [ [ argmode ] [ argname ] argtype [ { DEFAULT | = } default_expr ] [, ...] ] )
  { LANGUAGE lang_name
    | TRANSFORM { FOR TYPE type_name } [, ... ]
    | [ EXTERNAL ] SECURITY INVOKER | [ EXTERNAL ] SECURITY DEFINER
    | SET configuration_parameter { TO value | = value | FROM CURRENT }
    | AS 'definition'
    | AS 'obj_file', 'link_symbol'
    | sql_body
  }

1. A procedure is generated in the schema if a schema name is provided. Otherwise, the existing schema captures the newly built one within itself.
2. CREATE or REPLACE PROCEDURE can be used to change/replace the existing definition of the current procedure. The ownership and permissions will not change.
3. You must have USAGE privilege on the argument types to build a procedure.
4. The user who creates the procedure becomes the procedure’s owner.

The syntax given above is more generic to stored procedures. The one below is for PostgreSQL. 

create [or replace] procedure procedure_name(parameter_list)
language plpgsql
as $$
declare
-- variable declaration
begin
-- stored procedure body
end; $$
Code language: SQL (Structured Query Language) (sql)

Let’s break down the components In this syntax:

• Write the name of the stored procedure after the create procedure keywords.
• Set the parameters for the stored procedure. If not, a stored procedure can accept zero as well.
• Mention plpgsql as the procedural language for the stored procedure.
• Utilize the dollar-quoted string constant syntax to write the body of the stored procedure.

Note that parameters in stored procedures can’t have the out mode, but in and inout modes. As a stored procedure can’t return a value, you won’t be able to use the return statement with a value inside a store procedure like this:

return expression;
Code language: JavaScript (javascript)

But to stop the stored procedure immediately, you can utilitze the return statement without the expression as given: 

return;
Code language: SQL (Structured Query Language) (sql)

Workflow Example

Let’s use a stored_Procedure_Prac table to understand the PostgreSQL Stored Procedure better. We will use an online editor, OneCompiler, to write and run PostgreSQL queries for demo purposes.

Step 1: Create a table with the following inputs, as shown in the code block below.

create table stored_Procedure_Prac (
    id int generated by default as identity,
    name varchar(100) not null,
    balance dec(15, 2) not null,
    primary key(id)
);

insert into stored_Procedure_Prac(name, balance)
values('Don', 400000);

insert into stored_Procedure_Prac(name, balance)
values('Bob', 400000);

Step 2: Now run an SQL query to show the table.

select * from stored_Procedure_Prac;

The following shall be the result:

Step 3: The query below produces a stored procedure called prac_transfer, which transfers a specific amount of money from one account to another.

create or replace procedure prac_transfer(
   sender int,
   receiver int, 
   amount dec
)
language plpgsql    
as $$
begin
    -- subtracting the amount from the sender's account 
    update accounts 
    set balance = balance - amount 
    where id = sender;

    -- adding the amount to the receiver's account
    update accounts 
    set balance = balance + amount 
    where id = receiver;

    commit;
end;$$;

Step 4: Now call a stored procedure. Use the below-given query; a CALL statement is used.

call prac_transfer(1, 2, 1000);

The result would look like this:

Step 5: Now verify the results by running the following query.

SELECT * FROM stored_Procedure_Prac;

PostgreSQL Stored Procedure vs Function

A function returns a result, but a stored procedure does not. The reason is simple: the sole purpose of a stored procedure is to proceed with an action to complete it. Post that, the control is returned to the caller.

Do you know? Before PostgreSQL 11, stored procedures were functions that did not return data.

Using one of the PostgreSQL Stored Procedures examples query, let’s distinguish:

PostgreSQL Stored Procedures’ Query 

CREATE PROCEDURE deactivate_unpaid_accounts()
LANGUAGE SQL
AS $$
  UPDATE accounts SET active = false WHERE balance < 0;
$$;

For calling purposes, post PostgreSQL 11, we use the CALL statement as shown below:

CALL deactivate_unpaid_accounts();

PostgreSQL Function’s Query

CREATE FUNCTION deactivate_unpaid_accounts() RETURNS void
LANGUAGE SQL
AS $$
  UPDATE accounts SET active = false WHERE balance < 0;
$$;

For calling purposes, we used the SELECT statement, not CALL statement, as shown below:

SELECT deactivate_unpaid_accounts();

How Do PostgreSQL Stored Procedures Affect Your Workflow (Advantages vs Disadvantages)?

Advantages	Disadvantages
As stored Procedures can be reintroduced as often as possible, the number of visits between application and database servers is dramatically reduced.	Using PostgreSQL Stored Procedures can slow down the software development process because stored procedure programming necessitates specific abilities that many developers lack. (This is a human resources challenge)
To retrieve the results and remove the waiting time to get a response, now the app simply has to issue a function call instead of sending SQL statements.	It is difficult to manage workflow as many versions exist, and difficulty when debugging can not be undermined either.
The application’s performance is increased. The user-defined functions and stored procedures are now pre-combined in the PostgreSQL database server.	A portability issue exists. Other DBMS systems like MySQL and MS SQL Server are not supported.

Conclusion

This article provided an in-depth knowledge of PostgreSQL Stored procedures. Through this article and a workflow example, we learned to CREATE OR REPLACE a stored procedure. We also discussed how Stored Procedures are different from Functions.

If you want to continue your learning of PostgreSQL Commands and operations, go through either of the two articles provided below:

1. The Ultimate Guide to PostgreSQL Subquery for 2022
2. PostgreSQL MAX() Function: Syntax, Working & Examples

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FAQ on PostgreSQL Stored Procedures

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