Duplicate entry '111-222' for key 'PRIMARY' when inserting a new value to MySQL database - mysql

Question

I have a MySQL table running on AWS RDS with structure like the following:
CREATE TABLE `my_table` (
`col1` int(11) NOT NULL,
`col2` int(11) NOT NULL DEFAULT '0',
`f_name` varchar(45) DEFAULT NULL,
`l_name` varchar(45) DEFAULT NULL,
PRIMARY KEY (`col1`,`col2`),
KEY `idx_col1` (`col1`),
KEY `idx_col2` (`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
The query
SELECT * FROM my_table WHERE col1=111 AND col2=222;
returns 0 row.
But when I run an insert query
INSERT INTO my_table
(col1, col2, f_name, l_name)
VALUES (111, 222, 'John', 'Doe')
I got an error saying
Duplicate entry '111-222' for key 'PRIMARY'.
Why does this happen? The table doesn't contain a row with col1=111 and col2=222.
There's already a row with values col1=111, col2=111, f_name='John', and l_name='Doe'. But I don't think this would cause a duplicate entry error.
=========================== EDIT ======================================
There's a trigger that generates the duplicate error. Here's the script to reproduce the error.
# Initialize the tables
CREATE TABLE `my_table` (
`col1` int(11) NOT NULL,
`col2` int(11) NOT NULL DEFAULT '0',
`f_name` varchar(45) DEFAULT NULL,
`l_name` varchar(45) DEFAULT NULL,
PRIMARY KEY (`col1`,`col2`),
KEY `idx_col1` (`col1`),
KEY `idx_col2` (`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `triggered_table` (
`col1` int(11) NOT NULL,
`col2` int(11) NOT NULL DEFAULT '0',
`update_date` bigint(20) DEFAULT NULL,
PRIMARY KEY (`col1`,`col2`),
KEY `idx_col1` (`col1`),
KEY `idx_col2` (`col2`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
# Insert the data that cause duplicate error
INSERT INTO triggered_table (col1, col2) VALUES (111, 222);
# Create the trigger
DELIMITER $$
CREATE TRIGGER weird_trigger AFTER INSERT
ON my_table
FOR EACH ROW
BEGIN
INSERT INTO triggered_table
(col1, col2)
VALUES (NEW.col1, NEW.col2);
END$$
DELIMITER ;
# Create the duplicate error
INSERT INTO my_table
(col1, col2, f_name, l_name)
VALUES (111, 222, 'John', 'Doe');
I really don't understand why the developers created the triggered_table table. Why didn't they put update_date column to my_table?
This is so weird.

Answer 1

All you have to do is:
Truncate your table then run (Assuming that you have only a test data but if not, you have to do some backup first)
INSERT INTO my_table
(col1, col2, f_name, l_name)
VALUES (111, 222, 'John', 'Doe')
Now if the error still exists, this is a pretty much problem.
Your error seems like you concatinated col1 and col2 as your primary key ('111-222')
You can try
select * from yourTable where FieldPrimary = '111-222' if it is already exists

Answer 2

The duplicate key error does not come from the my_table table but from the triggered_table table instead. When you add a row in triggered_table for the key (111, 222) and then add a new row in the my_table table (with the same key), your trigger will also try to add a new row with the key (111, 222) in your triggered_table. However there is already such a key in use and you will get the duplicate key error.
Depending on what you want to do with the my_table and triggered_table tables, you might want to change the trigger to use REPLACE INTO instead of INSERT INTO. Or you run a check with SELECT first to see if you need to add a new row or not. After that you can run an UPDATE query to change the value of update_date. But to answer your question, the duplicate key error comes from the duplicate key in the triggered_table table.