I have a Existing column called CREATED DATE whose data type is "Date". I am trying to add a constraint to this CREATED DATE Column which will store "Record created time stamp". I have a following query in place but its working out. Any suggestions will be helpful.
ALTER TABLE CONTAINER_SCAN_LOG
MODIFY (CREATED_DATE DEFAULT (sysdate());
what is the error exactly ? what is the default date? anyway try to remove the parenthesis
ALTER TABLE ex_employee
MODIFY START_TIME DEFAULT (sysdate);
use timestamp instead of date
alter table t add (created_datetime timestamp default systimestamp)
or modify existing created_date to be of timestamp datatype and systimestamp default
Related
Working on hive table, where I need to change column name as below, its working as expected and changing column name but underline value of this column getting NULL.
ALTER TABLE db.tbl CHANGE hdfs_loaddate hdfs_load_date String;
Here changed column name is hdfs_load_date and values are getting NULL after renaming column name.
Does any one have idea to fix this. Thanks in advance!!
#Ajay_SK Referencing this article: Hive Alter table change Column Name
There is a comment:
Note that the column change will not change any underlying data if it is a parquet table. That is, if you have data in the table already, renaming a column will not make the data in that column accessible under the new name: select a from test_change; 1 alter table test_change change a a1 int; select a1 from test_change; null
He is specific to parquet, but the scenario you describe is similar where you have successfully changed the name, but hive still thinks the original data is in the original key.
A better approach to solve your issue, would be to create a new table of the schema you want with column name change. Then perform an Insert INTO new table select FROM * old table.
i have a table in apex oracle, i have a goal, constantly see the current date and time in the table after updating it. Someone can tell you how to do it.
For example:
Current date
10.10.2019 16:20:39
And after updating this table:
Current date
10.10.2019 16:21:39
You can use this syntax :
ALTER TABLE tab MODIFY current_date DEFAULT SYSDATE
provided your table already has current_date column of date type,
Use ALTER TABLE tab ADD current_date DATE DEFAULT SYSDATE if it's a non-existing column yet.
You can use triggers to achieve what you wanted. triggers are queries which fire on any CRUD actions.
So according to your scenario you need to create a trigger to update the current date and time column when updating your table row.
Hope this might help you
http://www.mysqltutorial.org/mysql-triggers.aspx
create table my_table(
id NUMBER(5),
my_date TIMESTAMP(3) DEFAULT CURRENT_TIMESTAMP,
constraint customers_pk primary key (id)
);
I want to make the TIMESTAMP like this: 'YYYY-MM-DD HH24:MI:SS',
and what does the number in brackets of timestamp mean?
timestamps don't have a format.
They are stored in a binary representation. If you want to display the values in a specific format, use to_char() to format it as a string or do that in your application.
as far as I know, you cannot change its format on CREATE TABLE.
on querying if you use proper NLS Format, you wont deal with this again and again
I'd like to add a NOT NULL column to a table called server. Problem is, the table already contains records. When I invoke ALTER TABLE server ADD COLUMN full_discovery_duration BIGINT NOT NULL H2 complains that full_discovery_duration may not be null. I can work around the problem by specifying DEFAULT 0 but I don't want a default valuefor future inserts. What am I supposed to do?
Should I add the column with a default and then remove DEFAULT 0 from the column definition in a subsequent statement? Is there a better way?
You can first add the column with a default value, and then set the default to null. Getting rid of the default definition is not possible however as far as I know.
An alternative is to first allow null, then set the values, and later not allow nulls.
drop table server;
create table server(id int);
insert into server values(1);
alter table server
add column
full_discovery_duration bigint;
update server set full_discovery_duration = 0;
alter table server
alter column
full_discovery_duration set not null;
While adding columns to existing tables, it should either be a nullable column or a default value must be specified. And what do you mean by removing the default? how can you remove value from a not null column?
I have created a table in oracle XE, and I have a field with type date. I would like if possible when I insert a row, that it automatically fills that field with the current date from the system.
I am inserting the rows from the SQL prompt.
Thanks
Here is how, you need to format your table properly:
create table test (first number
, second timestamp default systimestamp
, third varchar2(12));
And your default value is always current system time formatted as timestamp.
change the field after creating the table
ALTER TABLE table MODIFY time_collumn TIMESTAMP DEFAULT CURRENT_TIMESTAMP;
Or you could also use a trigger:
CREATE OR REPLACE TRIGGER date_trigger
BEFORE INSERT
ON table_name
REFERENCING NEW AS NEW
FOR EACH ROW
BEGIN
SELECT sysdate INTO :NEW.column_name FROM dual;
END;
The below snippet might be helpful if we forget to add the constraint while creating the table:
ALTER TABLE TABLE_NAME
ADD CONSTRAINT CONSTRAINT_NAME
COLUMN_NAME DATA_TYPE DEFAULT CURRENT_DATE;