Creating an SQL FUNCTION that inserts data into two existing tables - sql

Question

I am trying to create a FUNCTION that will insert complete and relevant information into an existing table. I need the FUNCTION to check if certain entities exist in another table and, if not, inserts the data. Example code below:
CREATE FUNCTION insert_payment (customer_uuid uuid, customer_name varchar(63), payment_uuid uuid, total_amount integer
So let's say that I wanted to enter a payment into a table called Payments. I want the FUNCTION to check another existing table called Customers to see if customer_uuid and customer_name already exist within the table. If not, I would like the FUNCTION to insert the customer_uuid and customer_name information into Customers as well as enter the data from all four parameters into Payments.
This is my first question to ask on Stack Overflow so if greater clarification is needed please let me know. I am also a student and still learning how to communicate effectively when talking about coding so, again, if further clarification is needed I will try my best. Thank you!

Answer 1

You can make use of an insert on conflict do nothing to insert the customer and skip inserting if it already exists.
So with this table definition:
create table customer (id uuid primary key, name text);
create table payment (id uuid primary key, customer_id uuid not null references customer, amount integer);
This function would do what you want:
CREATE FUNCTION insert_payment (customer_uuid uuid, customer_name varchar(63),
payment_uuid uuid, total_amount integer)
returns void
as
$$
insert into customer (id, name)
values (customer_uuid, customer_name)
on conflict do nothing;
insert into payment (id, customer_id, amount)
values (payment_uuid, customer_uuid, total_amount);
$$
language sql;
This is just as efficient as first checking the existence (select exists (...)) before inserting, because the INSERT statement will do that check anyway.
Online demo

Answer 2

I can help you more after knowing your table fields name but here I'm sharing a code maybe it'll help you
//set variable
$customer_uuid= $_POST['customer_uuid'];
$customer_name= $_POST['customer_name'];
//WRITE QUERY to the check-in customers table
$duplicate_customer = $this->db->prepare( "SELECT customer_uuid,customer_name FROM customers WHERE customer_uuid = '$customer_uuid' AND customer_name='customer_name'" ); $duplicate_customer->execute();
//now check data if exist in the customer table
if($duplicate_customer->rowCount() > 0){
//write here insert query to insert data in customer table
}