I understand how to keep default value as current timestamp, But I have requirement to replace NULL value in timestamp column with custom date/timestamp.
There is coalesce function that you can use, e.g.,
select coalesce(column_name, cast("2020-07-28 12:34:56" as timestamp))
Related
I'm having problems creating a table that should be pretty straightforward. The SQL code (Snowflake) is:
create or replace table bank_raw as
select
*,
created_at datetime default current_timestamp()
from bank_raw;
My error is: Syntax error: unexpected 'DEFAULT'. (line 12).
I don't know how I can recreate this table and add this default timestamp column. By the way, I have already created multiple tables from scratch with created_at DateTime default current_timestamp().
Any ideas?
It is possible to define column list definition when using CTAS:
Sample data:
CREATE TABLE bank_raw(id INT, col TEXT);
INSERT INTO bank_raw(id, col) VALUES (1, 'a'), (2,'b');
Query:
CREATE OR REPLACE TABLE bank_raw(id INT,
col TEXT,
created_at datetime default current_timestamp())
AS
SELECT
id, col, CURRENT_TIMESTAMP()
FROM bank_raw;
Output:
SELECT * FROM bank_raw;
DESCRIBE TABLE bank_raw;
Since this is a DML operation not a DDL operation, the default keyword does not apply. You can simply remove it and instead project the column and name it:
create or replace table bank_raw as
select
*,
current_timestamp() as created_at
from bank_raw;
Edit: To enforce a default, you cannot alter a table to add a column with a default value except for sequences. So you'd need to do something like this:
select get_ddl('table','BLANK_RAW');
-- Copy and paste the DDL. Rename the new table,
-- and add the default timestamp:
create or replace table A
(
-- Existing columns here then:
created_at timestamp default current_timestamp
);
You can then do an insert from a select on the table BLANK_RAW. You'll need to specify a column list and omit the CREATED_AT column.
Adding a column to one of my tables like this :
ALTER TABLE MY_TABLE
ADD S_CHANGED TIMESTAMP NOT NULL GENERATED ALWAYS FOR EACH ROW ON UPDATE AS ROW CHANGE TIMESTAMP
leads to an initial S_CHANGED value of zero (year zero) for existing rows.
Is there a way to specify a default value (e.g. CURRENT_TIMESTAMP) within the same SQL query, or is an UPDATE query required for that? Adding DEFAULT CURRENT_TIMESTAMP causes an error.
I have a database that I'm trying to add a column to. This column should hold information of the type timestamp, and I want every row to have the same timestamp (the current time) when I'm done.
I currently have tried:
cursor.execute('''ALTER TABLE my_table ADD COLUMN time timestamp DEFAULT ?''', (datetime.datetime.utcnow(),))
Which results in sqlite3.OperationalError: near "?": syntax error.
So then I tried:
cursor.execute(f'''ALTER TABLE my_table ADD COLUMN time timestamp DEFAULT {datetime.datetime.utcnow()}''')
Which results in sqlite3.OperationalError: near "-": syntax error.
Also, doing
cursor.execute(f'''ALTER TABLE my_table ADD COLUMN time timestamp DEFAULT CURRENT_TIMESTAMP''')
results in sqlite3.OperationalError: Cannot add a column with non-constant default.
How can I add the new column and set the values in that column? (Either through DEFAULT, or some other mechanism.)
SQLite does not allow adding a new column with a non-constant value. So this:
alter table my_table add column my_time timestamp default current_timestamp;
... generates error:
Cannot add a column with non-constant default
A simple option would be to recreate the table. Assuming that you have single column called id, that would look like:
create table my_table_new(
id int primary key,
my_time timestamp default current_timestamp
);
insert into my_table_new(id) select id from my_table;
drop table my_table; -- back it up first !
alter table my_table_new rename to my_table;
You can first add the new column and then update every existing row in the table to the desired value:
ALTER TABLE my_table ADD COLUMN time;
UPDATE my_table SET time = CURRENT_TIMESTAMP;
In Rails I created a string column called open_time, but then I realized I should use the datetime type. I did:
change_column :polls, :open_time, :datetime
But it said:
PG::Error: ERROR: column "open_time" cannot be cast to type timestamp without time zone
: ALTER TABLE "polls" ALTER COLUMN "open_time" TYPE timestamp
If I just drop the string column and add new datetime column, I will lose the data stored in the string column. Alternatively, in PostgreSQL I can add a column:
ALTER TABLE polls ADD COLUMN published_time timestamp;
Ant then try to get the data from the string column like:
UPDATE polls SET published_time = strToTimeStamp(open_time);
Are there any functions I can use as strToTimeStamp to convert character varying type to timestamp without time zone?
.. are there any functions I can use as strToTimeStamp that can convert
character varying type to timestamp without time zone type?
Use to_timestamp() to convert string data to type timestamp and alter the data type of the column in place:
ALTER TABLE tbl ALTER COLUMN col TYPE timestamp
USING to_timestamp(col, '<your pattern here>');
See:
Alter character field to date
Cast varchar type to date
Don't think you can do that, since it's limited by capability of database. The idea is doing following:
Created a new column with a different name
Copy over the column contents after data convert for each row
Drop the original col
Rename the new col to to the original col name
These steps can be placed into same migration file and keep them into a transaction for in case.
Is there some way mysql can store timestamp automatically in a record row whenever that it is created. I was trying to use timestamp(data type) with current_timestamp as default value but then realised this will get updated everytime the record is updated. I just need something that will store create timestamp.
Thanks
Set the DEFAULT constraint to use CURRENT_TIMESTAMP:
CREATE TABLE ...
your_date_column DATETIME DEFAULT CURRENT_TIMESTAMP
...
For an existing table, use the ALTER TABLE statement:
ALTER TABLE your_table
ALTER COLUMN date_column SET DEFAULT CURRENT_TIMESTAMP
Unless you specify a value to for the date_column, the default will be the date & time the INSERT statement was run. NULL and DEFAULT or valid values to use the default constraint otherwise, assuming the column is nullable.
You can get the full details on timestamps in MySQL at https://dev.mysql.com/doc/refman/5.0/en/timestamp-initialization.html.
The point that you care about is that if you define a timestamp column as DEFAULT CURRENT_TIMESTAMP clause and don't have an ON UPDATE clause, the column has the current timestamp for its default value but is not automatically updated.
But be warned. The obvious thing to want to do is to have two timestamp columns, one being the creation time and the other being the last update time. Unfortunately it is a documented MySQL limitation that MySQL does not support this. I have no idea why MySQL has such an odd limitation - no other major database has problems with this common use case.
FYI = "Datetime" is date and time fixed. "Timestamp" is variable date and time-- system time.
So, Have two columns. One Create Col, One Update Col.
The following command will create a hello table
1. id integer
2. create_at with current time.
create table hello (id int, created_at datetime DEFAULT CURRENT_TIMESTAMP);
Create Table myTableName
(
userId int primary key
userJoiningDate TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
https://www.mysqltutorial.org/mysql-timestamp.aspx
Here is how you can create a column in which the time stamp is recorded when it is created. If you want to know How to update timeStamp each time that row is changed/updated, Check the above link.
SELECT * FROM test WHERE timestamp >= CURDATE() AND timestamp < CURDATE() + INTERVAL 1 DAY ORDER BY timestamp;