MySQL Auto Update Date when any row value is updated - mysql

Question

I have an existing table with values already filled in. Last column is of type date.
My requirement is that if any value is updated, that row's corresponding date column should be automatically updated to the current date.
For example, if the table is as follows:
and if I change any of the values of col1 (78) /col2 (nvvb) /col3 (566) of say row no. 2 on date 18Nov2018, then the col4 of row 2 should automatically update to today's date of 18Nov2018 from existing 13-Oct-17.
I've checked existing topics by could not find an answer.
The closest I can find is this code, but it is not working for the above requirement:
create table if not exists my_table (
index1 char(32) not null primary key,
title varchar(50),
my_timestamp timestamp not null default current_timestamp on update current_timestamp
)
Any help will be greatly appreciated.
Thanks

Answer 1

First, you need to create code blocks for whatever code you are displaying in your question/answer by highlighting the lines of code and pressing ctrl-k
You will need a trigger that changes the date value in the row to the current date using the CURDATE() function. BEFORE UPDATE simply means apply the current block enclosed in "BEGIN... END" before the actual update call is made by MySQL. You access the row to be updated with NEW.<field>. To store a value in a particular tuple, use the SELECT ... INTO .... statement
DELIMITER $$
CREATE TRIGGER trigger_name
BEFORE UPDATE ON table_name
FOR EACH ROW
BEGIN
SELECT CURDATE() INTO NEW.`col4(date)`;
END $$
DELIMITER ;
For more info, see: https://dev.mysql.com/doc/refman/8.0/en/trigger-syntax.html
https://dev.mysql.com/doc/refman/8.0/en/ansi-diff-select-into-table.html
UPDATE: YOU CANNOT UPDATE WITHIN AN UPDATE TRIGGER, MySQL does not prevent an update trigger from being called by itself, nor does it prevent deadlock issues, so you cannot use this. Must use the method below.
Using the method described in the comments (if your version supports it):
CREATE TABLE last_mod (
last_modified_date DATE NOT NULL,
PRIMARY KEY (last_modified_date)
)
CREATE TABLE IF NOT EXISTS my_table (
my_date DATETIME NOT NULL,
INDEX par (my_date),
FOREIGN KEY (my_date) REFERENCES last_mod(mast_modified_date) ON UPDATE CASCADE
);
DELIMITER $$
CREATE TRIGGER trigger_name
BEFORE UPDATE ON my_table
FOR EACH ROW
BEGIN
UPDATE last_mod SET last_modified_date = CURDATE();
END $$
DELIMITER ;