How do you set a default value for a MySQL Datetime column?
In SQL Server it\'s getdate()
. What is the equivalant for MySQL? I\'m using MySQL 5.x if tha
Take for instance If I had a table named 'site' with a created_at and an update_at column that were both DATETIME and need the default value of now, I could execute the following sql to achieve this.
ALTER TABLE `site` CHANGE `created_at` `created_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP; ALTER TABLE `site` CHANGE `created_at` `created_at` DATETIME NULL DEFAULT NULL; ALTER TABLE `site` CHANGE `updated_at` `updated_at` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP; ALTER TABLE `site` CHANGE `updated_at` `updated_at` DATETIME NULL DEFAULT NULL;
The sequence of statements is important because a table can not have two columns of type TIMESTAMP with default values of CUREENT TIMESTAMP
I was able to solve this using this alter statement on my table that had two datetime fields.
ALTER TABLE `test_table`
CHANGE COLUMN `created_dt` `created_dt` TIMESTAMP NOT NULL DEFAULT '0000-00-00 00:00:00',
CHANGE COLUMN `updated_dt` `updated_dt` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP;
This works as you would expect the now() function to work. Inserting nulls or ignoring the created_dt and updated_dt fields results in a perfect timestamp value in both fields. Any update to the row changes the updated_dt. If you insert records via the MySQL query browser you needed one more step, a trigger to handle the created_dt with a new timestamp.
CREATE TRIGGER trig_test_table_insert BEFORE INSERT ON `test_table`
FOR EACH ROW SET NEW.created_dt = NOW();
The trigger can be whatever you want I just like the naming convention [trig]_[my_table_name]_[insert]
You can use triggers to do this type of stuff.
CREATE TABLE `MyTable` (
`MyTable_ID` int UNSIGNED NOT NULL AUTO_INCREMENT ,
`MyData` varchar(10) NOT NULL ,
`CreationDate` datetime NULL ,
`UpdateDate` datetime NULL ,
PRIMARY KEY (`MyTable_ID`)
)
;
CREATE TRIGGER `MyTable_INSERT` BEFORE INSERT ON `MyTable`
FOR EACH ROW BEGIN
-- Set the creation date
SET new.CreationDate = now();
-- Set the udpate date
Set new.UpdateDate = now();
END;
CREATE TRIGGER `MyTable_UPDATE` BEFORE UPDATE ON `MyTable`
FOR EACH ROW BEGIN
-- Set the udpate date
Set new.UpdateDate = now();
END;
I'm running MySql Server 5.7.11 and this sentence:
ALTER TABLE table_name CHANGE date_column datetime NOT NULL DEFAULT '0000-00-00 00:00:00'
is not working. But the following:
ALTER TABLE table_name CHANGE date_column datetime NOT NULL DEFAULT '1000-01-01 00:00:00'
just works.
As a sidenote, it is mentioned in the mysql docs:
The DATE type is used for values with a date part but no time part. MySQL retrieves and displays DATE values in 'YYYY-MM-DD' format. The supported range is '1000-01-01' to '9999-12-31'.
even if they also say:
Invalid DATE, DATETIME, or TIMESTAMP values are converted to the “zero” value of the appropriate type ('0000-00-00' or '0000-00-00 00:00:00').
CREATE TABLE `testtable` (
`id` INT(10) NULL DEFAULT NULL,
`colname` DATETIME NULL DEFAULT '1999-12-12 12:12:12'
)
In the above query to create 'testtable', i used '1999-12-12 12:12:12' as default value for DATETIME column colname
If you have already created the table then you can use
To change default value to current date time
ALTER TABLE <TABLE_NAME>
CHANGE COLUMN <COLUMN_NAME> <COLUMN_NAME> DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP;
To change default value to '2015-05-11 13:01:01'
ALTER TABLE <TABLE_NAME>
CHANGE COLUMN <COLUMN_NAME> <COLUMN_NAME> DATETIME NOT NULL DEFAULT '2015-05-11 13:01:01';