I want to edit a column in a MySQL table. Right now, it is tinyint with value NULL. I want to change the value to '0'. I tried using this expression:
ALTER TABLE hosts MODIFY COLUMN hide TINYINT NOT NULL DEFAULT 1;
and this
ALTER TABLE hosts MODIFY COLUMN hide TINYINT DEFAULT 1 NOT NULL;
and more variations. But this didn't work for me..
I get this error
EXECUTE FAIL:
ALTER TABLE hosts MODIFY COLUMN hide TINYINT(1) DEFAULT 0 NOT NULL
Message :
Invalid use of NULL value
What's the problem and what is the correct statement?
You cannot alter the table to „not null“ as long as you have data in it with null value.
First set all you data to 0
Update hosts set hide = 0 where hide is null
I want to assign a value as default for a column.
It says that there is a syntax error at line 2 :
SELECT `id` into #idND FROM `xxx` WHERE `name`='John';
ALTER TABLE `xxx2` CHANGE `statut_id` `statut_id` TINYINT(4) NULL DEFAULT #idND;
It works if I set DEFAULT 3 for example. What am I doing wrong please ?
For some reason, I have to change the default value of one parameter 'param' in a mysql table, I have to set it to NULL by default. I tried to manage it through phpmyadmin and I get this error message :
ALTER TABLE `mytable` CHANGE `param` `param` VARCHAR( 150 ) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT NULL
How can I resolve this ?
You can't set a NOT NULL column to have DEFAULT NULL.
In phpMyAdmin, check the Null? box for the column when editing it.
What is the difference between DEFAULT NULL and the CHECKBOX NULL mysql?
I can set default as NULL or there is a checkbox below which I can check to say NULL?
What's the difference?
Having a column DEFAULT NULL means if you don't set a value for the column, it will be NULL by default.
Having a column NULL(able) means it can be NULL at all, otherwise it will require you to set a value for the column, either by default or in the insert query. Only check that box if the value is supposed to be optional.
I hope this isn't a dumb question. You can set a default value for all variables or a function for when it is inserted. but if the field is not required to insert and you don't allow null values, what is the "blank" value that you see in phpMyAdmin? in a query is it returned as empty string, etc?
just trying to figure it out, I want to query for all records such that the value for a specific column in that record is not "empty" or blank or whatever.
thanks.
Referring to the manual,
For data entry for a NOT NULL column that has no explicit DEFAULT
clause, if an INSERT or REPLACE statement includes no value for the
column, or an UPDATE statement sets the column to NULL, MySQL handles
the column according to the SQL mode in effect at the time:
If strict SQL mode is not enabled, MySQL sets the column to the implicit default value for the column data type.
If strict mode is enabled, an error occurs for transactional tables and the statement is rolled back. For nontransactional tables, an
error occurs, but if this happens for the second or subsequent row of
a multiple-row statement, the preceding rows will have been inserted.
So your question now may be, what are the implicit default values for the various column data types? Here you go:
Implicit defaults are defined as follows:
For numeric types, the default is 0, with the exception that for integer or floating-point types declared with the AUTO_INCREMENT
attribute, the default is the next value in the sequence.
For date and time types other than TIMESTAMP, the default is the appropriate “zero” value for the type. For the first TIMESTAMP column
in a table, the default value is the current date and time. See Section 10.3, “Date and Time Types”.
For string types other than ENUM, the default value is the empty string. For ENUM, the default is the first enumeration value.
There IS no default value unless you specify one (i.e. unless you define a "default constraint" for the column in question).
Here's an example for adding a default on an existing column:
ALTER TABLE dbo.customer ALTER COLUMN contactname SET DEFAULT 'Unknown'
Here's an example creating the table with a default:
CREATE TABLE Books (
ID SMALLINT NOT NULL,
Name VARCHAR(40) NOT NULL,
PubID SMALLINT NOT NULL DEFAULT 0
)
It's good practice to declare ALL columns "not null", and provide default constraints as appropriate.
In the "books" example above, if you "insert" without specifying PubID, the PubID will be zero.
In the same example, if you "insert" without specifying ID or Name ... you'll get an error.
If you want MySQL to auto-assign an ID, use this syntax instead:
CREATE TABLE Books (
ID SMALLINT NOT NULL AUTO_INCREMENT,
Name VARCHAR(40) NOT NULL,
PubID SMALLINT NOT NULL DEFAULT 0
)
If you want to disallow null :-
alter table YOUR_TABLE modify column COLUMN varchar(255) not null default '';
The above query will disallow null and assign an empty string when the value is not supplied.
In phpmysqladmin, blank = empty.
Via PHP mysqli function or mysql function, null value is returned as null still.
Once you have apply the query, you can easily filter that by using
select ... from YOUR_TABLE
where COLUMN != ""; <-- no need to check is null
<-- because the first query already enforce not null
However, is best for you do this before perform the alter :-
update YOUR_TABLE set COLUMN = ""
where COLUMN is null;