I have a question related to the conversion of varchar to datetime.
This topic was covered already in the thread
SQL Server Convert Varchar to Datetime
but I would like to advance it bit further.
I have performed BULK INSERT into predefined tables where VARCHAR(255)
is the destination. I have a table dbo.USR_02_ALL_RAW and the field GLTGB which
holds strings in the following format: 07/16/2016.
I can convert it as a single string by the following code:
DECLARE #Date varchar(255)
set #Date= '07/16/2016'
SELECT CONVERT(datetime,RIGHT(#Date,4)+LEFT(#Date,2)+SUBSTRING(#Date,4,2))
and it gives me a result:
2016-07-16 00:00:00.000
However I would like to pass to the code the whole field GLTGB from the table
dbo.USR_02_ALL_RAW, convert it from VARCHAR into DATETIME and update the field GLTGB with these results.(converting the whole field from varchar to datetime)
Thank you!
First clear this, you want to Bulk insert or Bulk update. Since you already have a column GLTGB. If you want to update the value only.
update tab set GLTGB =
CONVERT(datetime,RIGHT(GLTGB,4)+LEFT(GLTGB,2)+SUBSTRING(GLTGB,4,2))
Or
If you want to update the field from varchar to datetime. Then process is little bit lengthy.
Alter table tab add newcol datetime --- Add new datetime type column
update tab set newcol =
CONVERT(datetime,RIGHT(GLTGB,4)+LEFT(GLTGB,2)+SUBSTRING(GLTGB,4,2)) --- update value in new column
Alter table tab drop column GLTGB --- drop GLGTB column
Alter table tab add GLGTB datetime --- add GLGTB column as datetime type
update tab set GLGTB = newcol --- update value from GLGTB from newcol
Alter table tab drop column newcol ---- remove unnecessary newcol
If you convert a value to datetime, then update the same database column it came from with the value then, since that column is still varchar, SQL will have to convert the value back to varchar again in order to store it. So you can't achieve anything useful with that kind of simple approach.
f you want to actually change the data type of the column, and also convert all the values, then I think you need to go through the following process:
1) Create a new varchar column in your table (which will be temporary)
2) copy all the data values from the GLTGB column into the new column (using an UPDATE statement)
3) Drop the GLTGB column
4) Re-create it with the same name but with datetime type
5) Use an UPDATE statement to re-populate the new GLTGB column from your temporary column
6) Finally, drop the temporary column
There may be a simpler way but that seems like the obvious process.
You can use the following code for updating but before that, you need to change the data type of your field to DateTime
update dbo.USR_02_ALL_RAW
set GLTGB=cast(CONVERT(datetime,RIGHT(#Date,4)+LEFT(#Date,2)+SUBSTRING(#Date,4,2)) as datetime)
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 that is a factor.
IMPORTANT EDIT:
It is now possible to achieve this with DATETIME fields since MySQL 5.6.5, take a look at the other post below...
Previous versions can't do that with DATETIME...
But you can do it with TIMESTAMP:
mysql> create table test (str varchar(32), ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
Query OK, 0 rows affected (0.00 sec)
mysql> desc test;
+-------+-------------+------+-----+-------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+-------------------+-------+
| str | varchar(32) | YES | | NULL | |
| ts | timestamp | NO | | CURRENT_TIMESTAMP | |
+-------+-------------+------+-----+-------------------+-------+
2 rows in set (0.00 sec)
mysql> insert into test (str) values ("demo");
Query OK, 1 row affected (0.00 sec)
mysql> select * from test;
+------+---------------------+
| str | ts |
+------+---------------------+
| demo | 2008-10-03 22:59:52 |
+------+---------------------+
1 row in set (0.00 sec)
mysql>
CAVEAT: IF you define a column with CURRENT_TIMESTAMP ON as default, you will need to ALWAYS specify a value for this column or the value will automatically reset itself to "now()" on update. This means that if you do not want the value to change, your UPDATE statement must contain "[your column name] = [your column name]" (or some other value) or the value will become "now()". Weird, but true. I am using 5.5.56-MariaDB
In version 5.6.5, it is possible to set a default value on a datetime column, and even make a column that will update when the row is updated. The type definition:
CREATE TABLE foo (
`creation_time` DATETIME DEFAULT CURRENT_TIMESTAMP,
`modification_time` DATETIME ON UPDATE CURRENT_TIMESTAMP
)
Reference:
http://optimize-this.blogspot.com/2012/04/datetime-default-now-finally-available.html
MySQL (before version 5.6.5) does not allow functions to be used for default DateTime values. TIMESTAMP is not suitable due to its odd behavior and is not recommended for use as input data. (See MySQL Data Type Defaults.)
That said, you can accomplish this by creating a Trigger.
I have a table with a DateCreated field of type DateTime. I created a trigger on that table "Before Insert" and "SET NEW.DateCreated=NOW()" and it works great.
For me the trigger approach has worked the best, but I found a snag with the approach. Consider the basic trigger to set a date field to the current time on insert:
CREATE TRIGGER myTable_OnInsert BEFORE INSERT ON `tblMyTable`
FOR EACH ROW SET NEW.dateAdded = NOW();
This is usually great, but say you want to set the field manually via INSERT statement, like so:
INSERT INTO tblMyTable(name, dateAdded) VALUES('Alice', '2010-01-03 04:30:43');
What happens is that the trigger immediately overwrites your provided value for the field, and so the only way to set a non-current time is a follow up UPDATE statement--yuck! To override this behavior when a value is provided, try this slightly modified trigger with the IFNULL operator:
CREATE TRIGGER myTable_OnInsert BEFORE INSERT ON `tblMyTable`
FOR EACH ROW SET NEW.dateAdded = IFNULL(NEW.dateAdded, NOW());
This gives the best of both worlds: you can provide a value for your date column and it will take, and otherwise it'll default to the current time. It's still ghetto relative to something clean like DEFAULT GETDATE() in the table definition, but we're getting closer!
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;
For all those who lost heart trying to set a default DATETIME value in MySQL, I know exactly how you feel/felt. So here is is:
ALTER TABLE `table_name` CHANGE `column_name` DATETIME NOT NULL DEFAULT 0
Carefully observe that I haven't added single quotes/double quotes around the 0
I'm literally jumping after solving this one :D
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';
MySQL 5.6 has fixed this problem.
ALTER TABLE mytable CHANGE mydate datetime NOT NULL DEFAULT 'CURRENT_TIMESTAMP'
this is indeed terrible news.here is a long pending bug/feature request for this. that discussion also talks about the limitations of timestamp data type.
I am seriously wondering what is the issue with getting this thing implemented.
You can use now() to set the value of a datetime column, but keep in mind that you can't use that as a default value.
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').
For all who use the TIMESTAMP column as a solution i want to second the following limitation from the manual:
http://dev.mysql.com/doc/refman/5.0/en/datetime.html
"The TIMESTAMP data type has a range of '1970-01-01 00:00:01' UTC to '2038-01-19 03:14:07' UTC. It has varying properties, depending on the MySQL version and the SQL mode the server is running in. These properties are described later in this section. "
So this will obviously break your software in about 28 years.
I believe the only solution on the database side is to use triggers like mentioned in other answers.
While defining multi-line triggers one has to change the delimiter as semicolon will be taken by MySQL compiler as end of trigger and generate error.
e.g.
DELIMITER //
CREATE TRIGGER `MyTable_UPDATE` BEFORE UPDATE ON `MyTable`
FOR EACH ROW BEGIN
-- Set the udpate date
Set new.UpdateDate = now();
END//
DELIMITER ;
Working fine with MySQL 8.x
CREATE TABLE `users` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`dateCreated` datetime DEFAULT CURRENT_TIMESTAMP,
`dateUpdated` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
PRIMARY KEY (`id`),
UNIQUE KEY `mobile_UNIQUE` (`mobile`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
Here is how to do it on MySQL 5.1:
ALTER TABLE `table_name` CHANGE `column_name` `column_name`
TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP;
I have no clue why you have to enter the column name twice.
While you can't do this with DATETIME in the default definition, you can simply incorporate a select statement in your insert statement like this:
INSERT INTO Yourtable (Field1, YourDateField) VALUES('val1', (select now()))
Note the lack of quotes around the table.
For MySQL 5.5
If you are trying to set default value as NOW(), I don't think MySQL supports that. In MySQL, you cannot use a function or an expression as the default value for any type of column, except for the TIMESTAMP data type column, for which you can specify the CURRENT_TIMESTAMP as the default.
I think it simple in mysql since mysql the inbuilt function called now() which gives current time(time of that insert).
So your query should look like similarly
CREATE TABLE defaultforTime(
`creation_time` DATETIME DEFAULT CURRENT_TIMESTAMP,
`modification_time` DATETIME default now()
);
Thank you.
If you set ON UPDATE CURRENT_TIMESTAMP it will take current time when row data update in table.
CREATE TABLE bar(
`create_time` TIMESTAMP CURRENT_TIMESTAMP,
`update_time` TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)
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
Use the following code
DELIMITER $$
CREATE TRIGGER bu_table1_each BEFORE UPDATE ON table1 FOR EACH ROW
BEGIN
SET new.datefield = NOW();
END $$
DELIMITER ;
If you are trying to set default value as NOW(),MySQL supports that you have to change the type of that column TIMESTAMP instead of DATETIME. TIMESTAMP have current date and time as default..i think it will resolved your problem..
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
This is my trigger example:
/************ ROLE ************/
drop table if exists `role`;
create table `role` (
`id_role` bigint(20) unsigned not null auto_increment,
`date_created` datetime,
`date_deleted` datetime,
`name` varchar(35) not null,
`description` text,
primary key (`id_role`)
) comment='';
drop trigger if exists `role_date_created`;
create trigger `role_date_created` before insert
on `role`
for each row
set new.`date_created` = now();
You can resolve the default timestamp. First consider which character set you are using for example if u taken utf8 this character set support all languages and if u taken laten1 this character set support only for English. Next setp if you are working under any project you should know client time zone and select you are client zone. This step are mandatory.
I have a SQL Server database and I'd like to change column types to reduce it's size:
I have a string Name Varchar(100) and want to convert it to Varchar(50) AND I have to move data to it (data will fit into varchar(50))
I have a Varchar(30) that represents time as epoch time (eg. 1508752574). I want to change the type to Datetime and convert data form Varchar(30) to Datetime and then put it in Datetime
Can I do it without losing data?
Point 1
ALTER TABLE dbo.table_name ALTER COLUMN name VARCHAR(50);
Point 2
You would need to add another column of type Datetime and update the column with the Datetime equivalent of the epoch_time_col.
ALTER TABLE dbo.table_name ADD epoch_time_dt DATETIME NULL;
UPDATE dbo.table_name SET epoch_time_dt = DATEADD(SECOND, epoch_time_col, '19700101');
If you need, you can then drop the old column
ALTER TABLE dbo.table_name DROP COLUMN epoch_time_col ;
Create new columns:
Alter table MyTable
add NewColumn1 varchar(50);
Alter table MyTable
add NewColumn2 datetime;
Fill with data:
update MyTable
set NewColumn1 = left(Name,50),
NewColumn2 = dateadd(s, epochcol1, '19700101');
You can then drop the old columns and rename the new ones
I don't see any loss of data issue..
I have a string Name Varchar(100) and want to convert it to Varchar(50) AND I have to move data to it (data will fit varchar(50))
There will be no data loss,if your data fits in varchar(50) data type,if the data doesn't fit the insert will fail and you can rectify that
Also i don't see any issue with data loss in converting your epoch value to datetime with below approach,since you are just adding seconds
Select
dateadd(S, [unixtime], '1970-01-01')
From [Table]
I have a column called MyYear that is of type datetime. It only stores the year though, so I want to change it to smallint.
When I try to run this:
ALTER TABLE MyTable
ALTER COLUMN MyYear smallint
I get this error:
Implicit conversion from data type datetime to smallint is not
allowed. Use the CONVERT function to run this query.
When I run this:
UPDATE MyTable
set MyYear=YEAR(MyYear)
It does something funky and sets all the years to 1905.
I am using SQL Server.
You cannot convert a DATETIME to a SMALLINT, you will need to:
ALTER TABLE MyTable
ADD MyActualYear SMALLINT
GO
UPDATE MyTable SET MyActualYear = CAST(YEAR(MyYear) AS SMALLINT)
GO
ALTER TABLE MyTable
DROP COLUMN MyYear
GO
EXEC sp_RENAME 'MyTable.[MyActualYear]' , 'MyYear', 'COLUMN'
GO
i.e. add a new temporary column, update it with the value you need, drop the old column and then rename the temp column with the original name.
If you have indexes on this column, you may want to bear in mind any impact this might have.
I am pretty new in Microsoft SQL Server and I am not so into DB in general.
I have the following doubt about an insert query that begin in this way:
insert into MyTable DEFAULT VALUES
What exactly mean the DEFAULT VALUES specification?
Tnx
Andrea
Reading the fine manual yields:
DEFAULT VALUES
Forces the new row to contain the default values defined for each column.
Well it uses the default values specified in your table.
So for example if you have a column CreationDate datetime default(getdate()) it will use it.
If each of the required columns in MyTable has specified DEFAULT VALUE then this statement insert such a row.
For example you could have column Date with default 01/01/2014 and position with DEFAULT 'Developer' and this statement would insert such a record.
You can read more here: http://msdn.microsoft.com/en-us/library/aa933206%28SQL.80%29.aspx
You can watch default specifications in work by checking that code:
DECLARE #tmp as table
(
id int null,
num int null default(777),
txt varchar(10) null default('abc'),
date datetime null
)
insert into #tmp DEFAULT VALUES
select * from #tmp
Output is
id num txt date
NULL 777 abc NULL