Conditional INSERT INTO statement in postgres

Question

I'm writing a booking procedure for a mock airline booking database and what I really want to do is something like this:

IF EXISTS (SELECT * FROM LeadCustomer 
    WHERE FirstName = 'John' AND Surname = 'Smith') 
THEN
   INSERT INTO LeadCustomer (Firstname, Surname, BillingAddress, email) 
   VALUES ('John', 'Smith', '6 Brewery close,
            Buxton, Norfolk', 'cmp.testing@example.com');

But Postgres doesn't support IF statements without loading the PL/pgSQL extension. I was wondering if there was a way to do some equivalent of this or if there's just going to have to be some user interaction in this step?

Answer 1

That specific command can be done like this:

insert into LeadCustomer (Firstname, Surname, BillingAddress, email)
select 
    'John', 'Smith', 
    '6 Brewery close, Buxton, Norfolk', 'cmp.testing@example.com'
where not exists (
    select 1 from leadcustomer where firstname = 'John' and surname = 'Smith'
);

It will insert the result of the select statement, and the select will only return a row if that customer does not exist.

Answer 2

As of 9.5 version of pgsql upsert is included, using INSERT ... ON CONFLICT DO UPDATE ...

The answer below is no longer relevant. Postgres 9.5 was released a couple years later with a better solution.

Postgres doesn't have " upsert " functionality without adding new functions.
What you'll have to do is run the select query and see if you have matching rows. If you do, then insert it.

I know you're not wanting an upsert exactly, but it's pretty much the same.

Answer 3

-- Use follwing format to insert data in any table like this --

create table user ( user_id varchar(25) primary key, phone_num numeric(15), failed_login int not null default 0, Login time timestamp );

INSERT INTO USER(user_id, phone_num, failed_login, Login time) VALUES ('12345','123456789','3',' 2021-01-16 04:24:01.755');