MySQL Convert data VARCHAR to DATETIME

Question

The table users was badly designed. The created_at and updated_at records were set with the VARCHAR type and the values were placed in them for a long time in the format like 20.10.2017 8:10 .

It is necessary to convert fields to the DATETIME type in MySQL, saving the values entered earlier.

The STR_TO_DATETIME function is not suitable because it changes the output format, but not the VARCHAR data type itself to DATETIME data type in the table.

ALTER TABLE users MODIFY created_at DATETIME

does not work

Error message:

SQL Error [1292] [22001]: Data truncation: Incorrect datetime value: '06.01.2020 8:10' for column 'created_at' at row 1

Answer 1

When you change a column from VARCHAR to DATETIME , there's no way for you to specify custom parsing of the string, it has to be in MySQL's default format.

So you'll need to do this in multiple steps:

1. Add a DATETIME column.
2. Fill in the new column by parsing the VARCHAR column with STR_TO_DATE()
3. Remove the old column and rename the new column.

ALTER TABLE users ADD created_at_dt DATETIME, updated_at_dt DATETIME;
UPDATE users
SET created_at_dt = STR_TO_DATE(created_at, '%d.%m.%Y %h:%i'),
    updated_at_dt = STR_TO_DATE(updated_at, '%d.%m.%Y %h:%i');
ALTER TABLE users 
    DROP created_at, DROP updated_at, 
    RENAME COLUMN created_at_dt TO created_at, RENAME COLUMN updated_at_dt TO updated_at;

Answer 2

The easiest way to work around this is to create new created_at and updated_at DATETIME columns, assign them the parsed date values, and then drop the old columns and rename the new ones. For example:

ALTER TABLE users ADD new_created_at DATETIME
UPDATE users SET new_created_at = STR_TO_DATE(created_at, '%d.%m.%Y %l:%i')
ALTER TABLE users DROP created_at, CHANGE new_created_at created_at DATETIME

Demo on dbfiddle

As @BillKarwin points out, you should check that new_created_at contains valid values before dropping the created_at column just in case some dates do not match the format. You can check for those cases using

SELECT *
FROM users
WHERE new_created_at IS NULL

And as @Barmar points out, it is preferable to try this first in a backup copy of the table.

Answer 3

You date has the false Format convert it to the correct mysql time and then alter the table

select version();

\n|  version() |\n|  :-------- | \n|  8.0.19 | \n

CREATE TABLE users (`created_at` varchar(20)) ; INSERT INTO users (`created_at`) VALUES ("06.01.2020 8:10"), ("07.01.2020 8:10"), ("08.01.2020 8:10"), ("09.01.2020 8:10")

\n✓ \n\n✓ \n

SELECT STR_TO_DATE(created_at, "%d.%m.%Y %k:%i") FROM users;

\n|  STR_TO_DATE(created_at, "%d.%m.%Y %k:%i") | \n|  :---------------------------------------- | \n|  2020-01-06 08:10:00 | \n|  2020-01-07 08:10:00 | \n|  2020-01-08 08:10:00 | \n|  2020-01-09 08:10:00 | \n

UPDATE users SET created_at = STR_TO_DATE(created_at, "%d.%m.%Y %k:%i");

\n✓ \n

SELECT * FROM users;

\n|  created_at | \n|  :------------------ | \n|  2020-01-06 08:10:00 | \n|  2020-01-07 08:10:00 | \n|  2020-01-08 08:10:00 | \n|  2020-01-09 08:10:00 | \n

ALTER TABLE users MODIFY created_at DATETIME

\n✓ \n

SELECT * FROM users;

\n|  created_at | \n|  :------------------ | \n|  2020-01-06 08:10:00 | \n|  2020-01-07 08:10:00 | \n|  2020-01-08 08:10:00 | \n|  2020-01-09 08:10:00 | \n

db<>fiddle here