SQLite, my references doesn't work - database

Question

I've a problem.
I want to create a table with 3 foreign key
PRAGMA foreign_keys = ON;
CREATE TABLE "Dipendente" ("idDipendente" INTEGER PRIMARY KEY AUTOINCREMENT,
"nome" VARCHAR NOT NULL,
"cognome" VARCHAR NOT NULL ,
"email" VARCHAR NOT NULL UNIQUE ,
"password" VARCHAR NOT NULL ,
"tipo" VARCHAR NOT NULL );
CREATE TABLE "Prodotto" ("idProdotto" INTEGER PRIMARY KEY AUTOINCREMENT,
"nome" VARCHAR NOT NULL UNIQUE,
"qta" INTEGER NOT NULL,
"prezzoUnita" FLOAT NOT NULL );
CREATE TABLE "Fondo" ("idFondo" INTEGER PRIMARY KEY AUTOINCREMENT,
"nome" VARCHAR NOT NULL UNIQUE,
"fondoDisponibile" FLOAT NOT NULL );
CREATE TABLE IF NOT EXISTS "Acquisto" (
`idAcquisto` INTEGER PRIMARY KEY NOT NULL ,
`idDipendente` INTEGER NOT NULL DEFAULT -1,
`idProdotto` INTEGER NOT NULL DEFAULT -1,
`idFondo` INTEGER NOT NULL DEFAULT -1,
`qta` INTEGER NOT NULL ,
`dataAcquisto` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ,
CONSTRAINT `fk_acquisto_dipendente`
FOREIGN KEY (`idDipendente` )
REFERENCES `Dipendente` (`idDipendente` )
ON DELETE SET DEFAULT
ON UPDATE NO ACTION,
CONSTRAINT `fk_acquisto_prodotto`
FOREIGN KEY (`idProdotto` )
REFERENCES `Prodotto` (`idProdotto` )
ON DELETE SET DEFAULT
ON UPDATE NO ACTION,
CONSTRAINT `fk_acquisto_fondo`
FOREIGN KEY (`idFondo` )
REFERENCES `Fondo` (`idFondo` )
ON DELETE SET DEFAULT
ON UPDATE NO ACTION);
CREATE INDEX 'fk_acquisto_dipendente' ON 'Acquisto' ('idDipendente' ASC);
CREATE INDEX 'fk_acquisto_prodotto' ON 'Acquisto' ('idProdotto' ASC);
CREATE INDEX 'fk_acquisto_fondo' ON 'Acquisto' ('idFondo' ASC);
So, I want to set Acquisto (idDipendente, idProdotto, idFondo) to -1 value by defaul, but when I delete the Dipendente's row with idDipendente = 1 in the table Acquisto the field idDipendente is set to 1 yet. I don't know what is the problem.

Answer 1

In the table "Acquisto", you have three foreign key references. Each column of those foreign key references has a default value of -1, which isn't (I presume) a valid value in any of the referenced tables.
In this specific case, if you first insert a row into "Dipendente", and that row has "idDipendente" of -1, then you can delete the row where "idDipendente" equals 1. When you do that, you'll find the default value of -1 in Acquisto.idDependente.
The short story is your foreign key reference doesn't prevent you from declaring a default value of -1, but it does prevent you from using it.
To set the values to NULL instead, you need to do something along these lines.
pragma foreign_keys = on;
create table a (id integer primary key);
insert into a values (1);
create table b (
b_id integer primary key,
a_id integer references a(id)
on delete set null);
insert into b values (1, 1);
delete from a;
select * from b;
b_id a_id
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