MySQL retrieve last_insert_id from stored procedure

Question

I am working with NodeJS and MySQL to save a post and its tags via post_tag:

DROP TABLE IF EXISTS post_tag;
DROP TABLE IF EXISTS post;
DROP TABLE IF EXISTS tag;
DROP PROCEDURE IF EXISTS select_all_posts;
DROP PROCEDURE IF EXISTS insert_post;

CREATE TABLE post (
  id INT NOT NULL AUTO_INCREMENT,
  title VARCHAR(45) NULL,
  body TEXT NULL,
  PRIMARY KEY (id));

CREATE TABLE tag (
  id INT NOT NULL AUTO_INCREMENT,
  tag VARCHAR(45) NULL,
  PRIMARY KEY (id));

CREATE TABLE post_tag (
  post_id INT NOT NULL,
  tag_id INT NOT NULL,
  PRIMARY KEY (post_id, tag_id),
  INDEX fk_post_tag_tag1_idx (tag_id ASC),
  INDEX fk_post_tag_post_idx (post_id ASC),
  CONSTRAINT fk_post_tag_post
    FOREIGN KEY (post_id)
    REFERENCES post (id),
  CONSTRAINT fk_post_tag_tag1
    FOREIGN KEY (tag_id)
    REFERENCES tag (id));

INSERT INTO post (id, title, body) VALUES (1, 'post 1', "Post body");
INSERT INTO post (id, title, body) VALUES (2, 'post 2', "Post body");
INSERT INTO tag (id, tag) VALUES (1, 'tag 1');
INSERT INTO tag (id, tag) VALUES (2, 'tag 2');
INSERT INTO post_tag (post_id, tag_id) VALUES (1, 1);
INSERT INTO post_tag (post_id, tag_id) VALUES (1, 2);
INSERT INTO post_tag (post_id, tag_id) VALUES (2, 1);

I created a stored procedure to insert new posts:

-- Stored procedure to insert post and tags
DELIMITER $$
CREATE PROCEDURE insert_post(
  IN title VARCHAR(45),
  IN body TEXT
)
BEGIN
  INSERT INTO post (title, body) VALUES (title, body);
END $$
DELIMITER ;

So in node I can do:

var mysql = require("mysql2");
var connection = mysql.createConnection({
  host: "127.0.0.1",
  user: "test_database",
  password: "test_database",
  database: "test_database",
});

connection.connect();

const postTitle = JSON.stringify("Post 3");
const postBody = JSON.stringify("This is post 3 body");
const insertPostQuery = "CALL insert_post(" + postTitle + "," + postBody + " )";

connection.query(insertPostQuery, (error, results) => {
  console.log(JSON.stringify(results, null, 4));
});

connection.end();

This returns:

{
    "fieldCount": 0,
    "affectedRows": 1,
    "insertId": 0,
    "info": "",
    "serverStatus": 2,
    "warningStatus": 0
}

Now I want to retrieve the last inserted id from the stored procedure, so I modify my stored procedure to add an OUT last_inserted_id INT param, and then assign it after the INSERT:

-- Stored procedure to insert post and tags
DELIMITER $$
CREATE PROCEDURE insert_post(
  IN title VARCHAR(45),
  IN body TEXT,
  OUT last_inserted_id INT
)
BEGIN
  INSERT INTO post (title, body) VALUES (title, body);
  SET last_inserted_id = LAST_INSERT_ID();
END $$
DELIMITER ;

But when executing the query in node this returns undefined instead of the json with the last_inserted_id value.

What I'm doing wrong?

Answer 1

Can you provide an example?

CREATE FUNCTION insert_post_fn(
  in_title VARCHAR(45),
  in_body TEXT
)
RETURNS BIGINT
MODIFIES SQL DATA
BEGIN
  INSERT INTO post (title, body) VALUES (in_title, in_body);
  RETURN LAST_INSERT_ID();
END

How to use:

SELECT insert_post_fn('Post title', 'This is post body') AS `LAST_INSERT_ID`;

---

CREATE PROCEDURE insert_post_proc(
  IN in_title VARCHAR(45),
  IN in_body TEXT,
  OUT out_id BIGINT
)
BEGIN
  INSERT INTO post (title, body) VALUES (in_title, in_body);
  SET out_id = LAST_INSERT_ID();
END

How to use:

CALL insert_post_proc('Post title', 'This is post body', @id);
SELECT @id AS `LAST_INSERT_ID`;
-- PS. Variable name used is random
-- PPS. Both statements must be executed 
--      in the same connection and without reconnect

---

CREATE PROCEDURE insert_post_proc(
  IN in_title VARCHAR(45),
  IN in_body TEXT
)
BEGIN
  INSERT INTO post (title, body) VALUES (in_title, in_body);
  SELECT LAST_INSERT_ID() AS `LAST_INSERT_ID`;
END

How to use:

CALL insert_post_proc('Post title', 'This is post body');

---

fiddle