I have a table which contains a couple timestamp fields and but I'm having some problems having some of the fields defaulting to NULL.
In my users table I have these timestamp tables:
(field),(NULL),(default val)
deleted_on YES NULL
last_change_attemp YES NULL
newpass_time YES NULL
last_login YES NULL
created NO 0000-00-00 00:00:00
updates YES NULL
When I go edit a row in phpMyAdmin, the row I'm editing already has the NULL checkbox checked for all NULL fields, except the first field: *deleted_on*. If I manually check the checkbox, it allows me to maintain that field as NULL.
When I update another field via a query, it automatically does a current_timestamp on that first field. Is this expected?
I've read through the docs again and noticed this piece of text
To specify automatic default or updating for a TIMESTAMP column other
than the first one, you must suppress the automatic initialization and
update behaviors for the first TIMESTAMP column by explicitly
assigning it a constant DEFAULT value (for example, DEFAULT 0 or
DEFAULT '2003-01-01 00:00:00'). Then, for the other TIMESTAMP column,
the rules are the same as for the first TIMESTAMP column, except that
if you omit both of the DEFAULT and ON UPDATE clauses, no automatic
initialization or updating occurs.
http://dev.mysql.com/doc/refman/5.0/en/timestamp.html
So for the time being I have the fields default to 0000-00-00 00:00:00 to prevent auto updates.
phpMyAdmin does some weird things with timestamps and null, especially if the column is marked as CURRENT_TIMESTAMP
I don't know why.
Related
I have a table with two timestamp fields. They are not nullable. The problem is that whenever I insert null into those fields, the current date is automatically saved, instead of throwing an error saying "Column 'first_data_dt' cannot be null", just like it happens when I insert a value into another non-nullable field.
There are no triggers associated to this table.
Does anybody know why this is happening?
EDIT to add table definition:
CREATE TABLE `ui_mytable` (
`id` int(11) NOT NULL,
`first_data_dt` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`last_data_dt` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00'
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
I understand now why first_data_dt is updated to the current timestamp anytime I insert null. But what about last_data_dt?
That's what a TIMESTAMP column does:
The TIMESTAMP data type offers automatic initialization and updating to the current date and time (that is, the current timestamp). [...] You can initialize or update any TIMESTAMP column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL attribute to permit NULL values.
Source: MySQL documentation
Maybe you want to use a DATETIME instead?
Creating a database table in MySQL. I have created two fields to grab timestamps.
created_at timestamp default '0000-00-00 00:00:00',
updated_at timestamp default now() on update now(),
When I update the database, both fields are updating to the current timestamp. Any thoughts on how to prevent this from happening? I am not providing the 'created_at' field when I update -- I am also providing 'null' for the updated_at field to auto update.
Depending on the version of MySQL you should be able to use the following for your default value on the updated_at field:
CURRENT_TIMESTAMP on UPDATE CURRENT_TIMESTAMP
Your created_at field should just have CURRENT_TIMESTAMP as the default.
I would also set both to the datatype datetime instead of timestamp.
Timestamp initialisation can be an ugly beast in mysql!
Based on the commment below you have mysql v5.6.4 or earlier:
I can't have two current_timestamps declared without getting an error -- and although it's default is 0 -- it is producing a current timestamp upon creation(without me feeding in the timestamp) – Spencer Rohan
You can have a single timestamp field that are initialised and/or updated to the current timestamp when you insert / update your record. In earlier versions this had to be the 1st timestamp field in the table.
I would simply set the created_at to be a nullable column with a default value of null because according to mysql documentation on timestamp initialization:
In other words, a TIMESTAMP column defined to permit NULL values auto-initializes only if its definition includes DEFAULT CURRENT_TIMESTAMP
By changing the default value to null you go around any problems you may have with zero dates and various sql modes.
created_at timestamp null default null,
I have this table with newspost, i want to add timestamps on date added, and i want to update another col when the post is edited. I would like it to happen automaticly in MySql. without the use of any PHP code.
CREATE TABLE IF NOT EXISTS news (
id int(11) NOT NULL AUTO_INCREMENT,
data text,
date_published timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
date_edited timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (id)
);
What's the best practice in a case like this?
Consider using triggers. From the MySQL docs:
A trigger is a named database object that is associated with a table, and that activates when a particular event occurs for the table. Some uses for triggers are to perform checks of values to be inserted into a table or to perform calculations on values involved in an update.
Example of a trigger:
CREATE TRIGGER trigger_example AFTER UPDATE ON news
FOR EACH ROW UPDATE some_table SET another_column = NEW.data;
You can only use the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP features on one timestamp column in a table.
Use the following table definition to turn off the features for date_published and use them for date_edited:
CREATE TABLE IF NOT EXISTS news (
id INT(11) NOT NULL AUTO_INCREMENT,
data TEXT,
date_published TIMESTAMP NOT NULL DEFAULT 0,
date_edited TIMESTAMP NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (id)
);
When inserting a new row, pass a NULL value for date_published to automatically assign the current timestamp to that column.
MySQL Docs on Automatic Initialization and Updating for TIMESTAMP:
It need not be the first TIMESTAMP column in a table that is
automatically initialized or updated to the current timestamp.
However, to specify automatic initialization or updating for a
different TIMESTAMP column, you must suppress the automatic properties
for the first one. Then, for the other TIMESTAMP column, the rules for
the DEFAULT and ON UPDATE clauses are the same as for the first
TIMESTAMP column, except that if you omit both clauses, no automatic
initialization or updating occurs.
To suppress automatic properties for the first TIMESTAMP column, do
either of the following:
Define the column with a DEFAULT clause that specifies a constant default value.
Specify the NULL attribute. This also causes the column to permit NULL values, which means that you cannot assign the current timestamp by setting the column to NULL. Assigning NULL sets the column to NULL.
I have a table with the below column
`update_ts` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
I have two databases set up using replication. On master while inserting null to the above column, Current time stamp is inserted.
But the same record on being replicated to the slave gives error. Error is that Null value is not permitted for the column
The only difference is that in slave DB, the specific column is indexed in the table.
Mysql reference has the below line
By default, TIMESTAMP columns are NOT NULL, cannot contain NULL values, and assigning NULL assigns the current timestamp.
So i expect the column to get the current time stamp
The data is put to master through spring.
Is this an expected behaviour?
tl;dr
The NOT NULL is permitting you to pass a null value which would normally become current_timestamp.
Original
Its inserted as "null". INSERT INTO table Values(null);
That's forbidden due to the NOT NULL requirement (the point with NOT NULL is to forbid null values) -- you're not suppose to mention the value. Skip the value and the default value will take it's correct place.
Let's take a look at the docs:
In addition, you can initialize or update any TIMESTAMP column to the current date and time by assigning it a NULL value, unless it has been defined with the NULL attribute to permit NULL values.
You are permitting null values because of your NOT NULL requirement. In order for your argument to be valid then you need to remove it.
Found the issue. The flag
explicit_defaults_for_timestamp
was not set in replication. Setting this solves the problem
I have a table with two timestamp fields. I simply defined them with a name and the type TIMESTAMP, yet for some reason MySQL automatically set one of them with a default value and the attribute on update CURRENT_TIMESTAMP. I was planning on having NO default value in either of the fields, but one of the fields is called "date_updated" so I suppose I could set the mentioned attribute to that field.
Unfortunately, it's the field "date_created" that was set with the on update CURRENT_TIMESTAMP attribute, and no matter what I do, MySQL won't let me remove it.
I've tried editing the "date_created" field and removing the attribute. When clicking save, the attribute is back. I have also tried selecting both fields, removing the attribute from one of them and setting it on the other. It gives me the error #1293 - Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause and suddenly both attribute columns on the values are set to on update CURRENT_TIMESTAMP the result:
Error
SQL query:
ALTER TABLE `pages` CHANGE `date_created` `date_created` TIMESTAMP NOT NULL ,
CHANGE `date_updated` `date_updated` TIMESTAMP ON UPDATE CURRENT_TIMESTAMP NOT NULL
MySQL said:
#1293 - Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT or ON UPDATE clause
Must I really recreate both those columns in the correct order to fix this?
I would like to know how I could solve this problem correctly, for future reference.
Thanks
Now I've also tried to run
ALTER TABLE pages
CHANGE date_created
date_created TIMESTAMP NOT NULL
You should specify DEFAULT CURRENT_TIMESTAMP (or DEFAULT 0)
ALTER TABLE pages CHANGE date_created date_created TIMESTAMP NOT NULL DEFAULT 0,
CHANGE `date_updated` `date_updated` TIMESTAMP ON UPDATE CURRENT_TIMESTAMP NOT NULL
As of MySQL version 5.6.6, you can use the explicit_defaults_for_timestamp option in the configuration file, therefore timestamp columns will not have 'DEFAULT CURRENT_TIMESTAMP' or 'ON UPDATE CURRENT_TIMESTAMP' attributes by default. It will also be possible so set these columns to NULL if they are not declared as NOT NULL.
See: http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html#sysvar_explicit_defaults_for_timestamp