Stored procedure to update parent in MySQL

Question

I have 2 tables for representing sensors and their values:

Unit:
  id
  name
  last_data

Data:
  id
  timestamp
  temperature
  unit

So basically I have multiple Data rows for each Unit .

I want to add a SP so every time I insert a Data row, it will automatically update last_data column in the matching parent (to point to the newly create id .

pseudo code:

new_id = INSERT INTO Data (temperature, unit) VALUES (25, 1);

UPDATE Unit SET last_data = new_id WHERE id=1

Not sure how to write such procedure...

Answer 1

You can use LAST_INSERT_ID() to get the ID of the last record that you've created within your session.

So you pseudo code would become something like:

INSERT INTO Data (temperature, unit) VALUES (25, 1);
SET @new_id = LAST_INSERT_ID();
UPDATE Unit SET last_data = @new_id WHERE id=1

Or even shorter:

INSERT INTO Data (temperature, unit) VALUES (25, 1);
UPDATE Unit SET last_data = LAST_INSERT_ID() WHERE id=1

https://dev.mysql.com/doc/refman/5.7/en/information-functions.html#function_last-insert-id

Answer 2

This can help you to solve you problem:

INSERT INTO Data (temperature, unit) VALUES (25, 1);

this our trigger:

CREATE TRIGGER update_last_data 
    AFTER INSERT ON 'Data' for each row
begin
    SET @last_id_in_data = LAST_INSERT_ID();
    UPDATE Unit SET last_data = @last_id_in_data WHERE id=1;
END;