PostgreSQL – CREATE PROCEDURE
Last Updated :
28 Aug, 2020
PostgreSQL CREATE PROCEDURE statement as the name suggests is used to create new stored procedures. So far, you have learned how to define user-defined functions using the create function statement.
A drawback of user-defined functions is that they cannot execute transactions. In other words, inside a user-defined function, you cannot start a transaction, and commit or rollback it. PostgreSQL 11 introduced stored procedures that support transactions. To define a new stored procedure, you use the create procedure statement.
The following illustrates the basic syntax of the create procedure statement:
Syntax:
create [or replace] procedure procedure_name(parameter_list)
language plpgsql
as $$
declare
-- variable declaration
begin
-- stored procedure body
end; $$
Let’s analyze the above syntax:
- First, specify the name of the stored procedure after the create procedure keywords.
- Second, define parameters for the stored procedure. A stored procedure can accept zero or more parameters.
- Third, specify plpgsql as the procedural language for the stored procedure. Note that you can use other procedural languages for the stored procedure such as SQL, C, etc.
- Finally, use the dollar-quoted string constant syntax to define the body of the stored procedure.
Parameters in stored procedures can have the in and inout modes. They cannot have the out mode. A stored procedure does not return a value. You cannot use the return statement with a value inside a store procedure like this:
return expression;
However, you can use the return statement without the expression to stop the stored procedure immediately:
return;
Example:
We will use the following accounts table for the demonstration:
drop table if exists accounts;
create table accounts (
id int generated by default as identity,
name varchar(100) not null,
balance dec(15, 2) not null,
primary key(id)
);
insert into accounts(name, balance)
values('Raju', 10000);
insert into accounts(name, balance)
values('Nikhil', 10000);
The following query will show the table data:
select * from accounts;
That depicts the result as shown below:
The following query creates a stored procedure named transfer that transfers a specified amount of money from one account to another.
create or replace procedure transfer(
sender int,
receiver int,
amount dec
)
language plpgsql
as $$
begin
-- subtracting the amount from the sender's account
update accounts
set balance = balance - amount
where id = sender;
-- adding the amount to the receiver's account
update accounts
set balance = balance + amount
where id = receiver;
commit;
end;$$
Calling a stored procedure
To call a stored procedure, you use the CALL statement as follows:
call stored_procedure_name(argument_list);
Example:
The below statement invokes the transfer stored procedure to transfer $1, 000 from Raju’s account to Nikhil’s account:
call transfer(1, 2, 1000);
The following statement verifies the data in the accounts table after the transfer:
SELECT * FROM accounts;
Output:
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