Insert statement in self-join table - mysql

Question

What is the correct statement to make an insert in a table with a self-join?
If I try to make a classic insert I get the error:
Cannot add or update a child row: a foreign key constraint fails
This is my insert query:
insert into mTable(record_name,self_fk,val, note, ref,insert_date, end_date)
values('processo prova',0,1,'nota di prova', 'az12345', NOW(), NOW());

Answer 1

In your INSERT query, you are referencing to a foreign key (the id 0) that doesn't exist -> constraint fails
I saw in your edits, before you roll it back, your CREATE TABLE script.
The field containing the reference to the parent was created this way :
`id_processo_padre` int(11) NOT NULL DEFAULT '1'
I suggest you to edit this field to make it nullable :
ALTER TABLE `mTable` MODIFY `id_processo_padre` int(11) NULL;
This will allow you to INSERT the first top level parent (or any top level parent)
insert into mTable(record_name, self_fk, ...)
values('processo prova', NULL, ...);
-- ^--^----------This
Test it yourself :
Schema (MySQL v5.7)
CREATE TABLE test
(
id INT(6) NOT NULL PRIMARY KEY AUTO_INCREMENT,
parent_id INT(6) NULL,
someData VARCHAR(255),
FOREIGN KEY (parent_id) REFERENCES test(id)
);
INSERT INTO test VALUES (default, null, "parent"),
(default, 1, "child1_1"),
(default, 1, "child1_2"),
(default, 3, "child2_2");
Query #1
SELECT t1.*, t2.someData AS "My parent's name" FROM test t1
LEFT JOIN test t2
ON t2.id = t1.parent_id
ORDER BY t1.id ASC;
Output
| id | parent_id | someData | My parent's name |
| --- | --------- | -------- | ---------------- |
| 1 | null | parent | null |
| 2 | 1 | child1_1 | parent |
| 3 | 1 | child1_2 | parent |
| 4 | 3 | child2_2 | child1_2 |
View on DB Fiddle