Create Column Allow NULL but Default Value Set to NOT NULL - mysql

Id like to create a column on my table that allows null but is set by default to empty (not null)
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} DEFAULT '';
This doesn't seem to work. Any ideas?
Thanks!


Did you try
ALTER TABLE table_name ADD column_name VARCHAR(20) NULL DEFAULT '';


If all else fails,
CREATE TRIGGER trigger_tablename_columnname
BEFORE INSERT ON tablename
FOR EACH ROW SET NEW.columnname = IFNULL(NEW.columnname, '')

Related

mysql, Create Column with a default value

I've a table item that has some columns that are nullable.
To one of them type, I'd like to automatically insert a default value (instead of a NULL) whenever a new record in inserted in the table and do not specify a value for that column.
Can it be done without affecting the existing data?
The type column is a varchar.
I can update the current nulls.

You can try to ALTER column set a default value.
ALTER TABLE `T` MODIFY `type` varchar(50) DEFAULT 'default';
then insert by DEFAULT keyword:
INSERT INTO T (type) VALUES (DEFAULT);
Results:

This query will work for you.
For update table.
ALTER TABLE `column_name` CHANGE `tab` `my_id` INT(11) NOT NULL DEFAULT '0';
For insert table
CREATE TABLE `db_name`.`Tbale_name` ( `demo` INT NOT NULL DEFAULT '0');

alter a table column to nullable

I want to alter a field to nullable and add the default value null.table name 'other_details' column name used_asset which is varchar(100)
ALTER TABLE `other_details` ALTER COLUMN `used_asset` varchar(100) DEFAULT NULL
above query shows error 'syntax error near varchar(100) DEFAULT NULL'

This came from phpmyadmin as preview SQL and it seems to work:
ALTER TABLE `other_details` CHANGE `used_asset` `used_asset` VARCHAR(100) NULL DEFAULT NULL;

Try this
1) Using MODIFY
ALTER TABLE `other_details` MODIFY `used_asset` varchar(100) null;
2) Using CHANGE
Syntax
ALTER TABLE table_name CHANGE column_name column_name type DEFAULT NULL
Example
ALTER TABLE `other_details` CHANGE `used_asset` `used_asset` varchar(100) DEFAULT NULL;

ALTER TABLE Table_Name MODIFY Column_Name DataType DEFAULT NULL;

Alter table add column and set default value in MySQL

Is there a way to add a new column and set its default value in MySQL? When I run this command I get a syntax error:
ALTER TABLE tableName ADD newColumn varchar(20) SET DEFAULT 'test';
The documentation I've found doesn't really help me.

The SET shouldn't be necessary:
ALTER TABLE tableName ADD newColumn varchar(20) DEFAULT 'test';

try this
ALTER TABLE tableName ADD COLUMN newColumn VARCHAR(20) DEFAULT 'test';

Alter mysql table default value and NULLvalue?

How can i make a table field with default value "none" and null value "no"?
When i create a table with following code it always add default value NULL and null to yes
ALTER TABLE `table_name` ADD `test` INT(11) AFTER `test1`

ALTER TABLE `table_name` ADD `test` INT NOT NULL AFTER `test1`;

ALTER TABLE myTable
ALTER column SET DEFAULT 'none'.
For replacing NULL with NO you don't have to alter the table just do it in your query :
SELECT COALESCE(columnWhichisNull,'no'))
FROM myTable ;
COALESCE checks if a value from a column is null and replaces it with your desired character

I can't modify a table's column in MySQL [duplicate]

I got the following error while trying to alter a column's data type and setting a new default value:
ALTER TABLE foobar_data ALTER COLUMN col VARCHAR(255) NOT NULL SET DEFAULT '{}';
ERROR 1064 (42000): You have an error in your SQL syntax; check the
manual that corresponds to your MySQL server version for the right
syntax to use near 'VARCHAR(255) NOT NULL SET DEFAULT '{}'' at line 1

ALTER TABLE foobar_data MODIFY COLUMN col VARCHAR(255) NOT NULL DEFAULT '{}';
A second possibility which does the same (thanks to juergen_d):
ALTER TABLE foobar_data CHANGE COLUMN col col VARCHAR(255) NOT NULL DEFAULT '{}';

As a follow up, if you just want to set a default, pretty sure you can use the ALTER .. SET syntax. Just don't put all the other stuff in there. If you're gonna put the rest of the column definition in, use the MODIFY or CHANGE syntax as per the accepted answer.
Anyway, the ALTER syntax for setting a column default, (since that's what I was looking for when I came here):
ALTER TABLE table_name ALTER COLUMN column_name SET DEFAULT 'literal';
For which 'literal' could also be a number (e.g. ...SET DEFAULT 0). I haven't tried it with ...SET DEFAULT CURRENT_TIMESTAMP but why not eh?

If you want to add a default value for the already created column,
this works for me:
ALTER TABLE Persons
ALTER credit SET DEFAULT 0.0;

For DEFAULT CURRENT_TIMESTAMP:
ALTER TABLE tablename
CHANGE COLUMN columnname1 columname1 DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
CHANGE COLUMN columnname2 columname2 DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP;
Please note double columnname declaration
Removing DEFAULT CURRENT_TIMESTAMP:
ALTER TABLE tablename
ALTER COLUMN columnname1 DROP DEFAULT,
ALTER COLUMN columnname2 DROPT DEFAULT;

In case the above does not work for you (i.e.: you are working with new SQL or Azure) try the following:
1) drop existing column constraint (if any):
ALTER TABLE [table_name] DROP CONSTRAINT DF_my_constraint
2) create a new one:
ALTER TABLE [table_name] ADD CONSTRAINT DF_my_constraint DEFAULT getdate() FOR column_name;

Accepted Answer works good.
In case of Invalid use of NULL value error, on NULL values, update all null values to default value in that column and then try to do the alter.
UPDATE foobar_data SET col = '{}' WHERE col IS NULL;
ALTER TABLE foobar_data MODIFY COLUMN col VARCHAR(255) NOT NULL DEFAULT '{}';

Try this
ALTER TABLE `table_name` CHANGE `column_name` `column_name` data_type NULL DEFAULT '';
like this
ALTER TABLE `drivers_meta` CHANGE `driving_license` `driving_license` VARCHAR(30) NULL DEFAULT '';

Use this approach:-
ALTER TABLE foobar_data
CHANGE COLUMN col VARCHAR(255) NOT NULL SET DEFAULT '{}';