你可以利用 insert on conflict do nothing 插入客户，如果客户已经存在，则跳过插入。
所以在这个表定义中：

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);

此函数将执行您想要的操作：

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;

这和首先检查是否存在一样有效( select exists (...) )在插入之前，因为insert语句无论如何都会执行该检查。
在线演示

在知道表字段的名称之后，我可以帮助您更多，但是在这里我共享一个代码，也许它会帮助您

//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
}