Alter table and set default as current date - mysql

Question

while creating a table I forgot to add a date of birth column. Is there a way to add a NOT NULL column to a table with default value being current date?

Answer 1

You can use alter table. In MySQL 8.0:
alter table mytable
add datetime_of_birth datetime
not null
default (current_date);
In earlier versions, you can't however, have a date column whose value defaults to current_date. This feature is supported for datetimes a and timestamps column only. If you can live with a datetime column, then:
alter table mytable
add datetime_of_birth datetime
not null
default current_timestamp;
You can then ignore the time portion of the column when querying it. If that's not an acceptable solution, then you need to implement the logic with a trigger.

Answer 2

Use alter table:
alter table t add column date_of_birth date;

Answer 3

If your table has rows of data in it, you must either add the column as nullable, or else give it a DEFAULT that will be assigned on every row.
If you don't give a DEFAULT, then a NOT NULL column will attempt to add the "default default." A date's default is '0000-00-00' which is an invalid date, and it will be rejected if you have strict mode set (which I do recommend):
mysql> create table mytable (id int primary key );
Query OK, 0 rows affected (0.02 sec)
mysql> insert into mytable values (1);
Query OK, 1 row affected (0.01 sec)
mysql> alter table mytable add column date_of_birth date not null;
ERROR 1292 (22007): Incorrect date value: '0000-00-00' for column 'date_of_birth' at row 1
The DATETIME or TIMESTAMP data types can be given a default of CURRENT_TIMESTAMP:
mysql> alter table mytable add column date_of_birth datetime not null default current_timestamp;
Query OK, 0 rows affected (0.13 sec)
Records: 0 Duplicates: 0 Warnings: 0
But you said you wanted a column that is DATE, which doesn't allow this:
mysql> alter table mytable add column date_of_birth date not null default current_timestamp;
ERROR 1067 (42000): Invalid default value for 'date_of_birth'
In MySQL 8.0, you can use expressions as defaults (note the extra parentheses around the expression, which are required):
mysql> alter table mytable add column date_of_birth date not null default (curdate());
Query OK, 1 row affected (0.04 sec)
Records: 1 Duplicates: 0 Warnings: 0
If you're using an earlier version of MySQL, then you can't do this in one ALTER TABLE. You must first add the column as a nullable column, then use UPDATE to backfill values into all the existing rows, then ALTER TABLE again to modify the column to be NOT NULL.