mysql automatically store record creation timestamp - sql

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;

Related

How to add timestamp column into existing table

I have a Postgres table with certain data, let's say I have 3 columns at the beginning:
name
age
gender
Name1
31
F
Name2
18
M
Name3
22
F
Later on I want to add a new field created_date to record when a user is created and meet 2 sceanrios:
For the existing users, leave the fields empty
For the new users, the field created_date is required and can't be NULL.
Now I can't find a way to how to define "empty" since it can't be null if I add created_date NOT NULL like below query, but the same time I don't want to add DEFAULT xxx since the time is inaccurate.
ALTER TABLE `users`
ADD `created_Date` DATETIME NOT NULL
DEFAULT '2023-02-03 00:00:00'
Can anyone help to define the "empty" in this case?

There are only three options:
Make the new column not nullable
Make the column nullable and use a default date for all existing entries like 01.01.2000. You can set a default value on the column or do an update after adding the column. In the second case the not null needs to be added (with alter table statement) to the column after the update statement.
Create a complete new Table and use it to insert new entries. To read all values together (old entries without date column and new columns with date column) you can make a View which combines the two tables with a union all. This case requires adjustments in your Application and a good thinking about to not have duplicate entries in both tables. And of course the sequences needs to be adjusted aswell. I would not go this way.
Unfortunately there is no other option if the column needs to be not null.

I'd recommend instead:
ALTER TABLE users
ADD COLUMN created TIMESTAMP WITH TIME ZONE NOT NULL
DEFAULT '1970-01-01 00:00:00 UTC';
ALTER TABLE users
ALTER COLUMN created SET DEFAULT now();
That's because:
The column name "current_date" is misleading. This is a timestamp, not just a date.
You should always use "timestamp with time zone" for timestamps, or you'll otherwise have various bugs, like values going backwards, being duplicated, jumping forward, being interpreted differently depending on the client's time zone etc.
This will fill currently existing rows with the timestamp '1970-01-01 00:00:00 UTC', which is immediately recognized as a timestamp "0", so called "epoch time", making it obviously fake, but still older than any newly created.
After that, changing the default to now() will make new rows fill the timestamp automatically and correctly, when the client will either skip the column or will use DEFAULT as value.

How to add column to database with default

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;

SQL - Multiple fields are updated instead of one

I have four columns: ID, STARTTIME, ENDINGTIME and DURATION.
The table is created with:
CREATE TABLE tableName (
ID INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT,
STARTTIME TIMESTAMP,
ENDINGTIME TIMESTAMP,
DURATION TIME);
The ID is an auto_increment column. Then I've the code for inserting a new STARTTIME:
INSERT INTO tableName(STARTTIME) VALUES(CURRENT_TIMESTAMP);
Secondly I've the code for updating the row with the biggest ID to set the ENDINGTIME:
SET #latestInsertID = (SELECT MAX(ID) FROM tableName);
UPDATE tableName SET ENDINGTIME=(CURRENT_TIMESTAMP) WHERE ID=#latestInsertID;
Now I can execute both (all three) queries without getting an exception and the first query works totally fine (as I expected). But the last query updates (from the row I wanted to update) the ENDINGTIME as well as the STARTTIME. Why doesn't it just update the ENDINGTIME?
Thank you for every solution!

Use DATETIME instead of TIMESTAMP (MWE)
Here's why:
The timestamp field is generally used to define at which moment in time a row was added or updated and by default will automatically be assigned the current datetime when a record is inserted or updated. The automatic properties only apply to the first TIMESTAMP in the record; subsequent TIMESTAMP columns will not be changed.

Educated guess. Column is defined as:
CREATE TABLE tablename(
-- ...
STARTTIME TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
);
Or there is underlying trigger that perfroms same logic.

Is it possible to get last update time of the row in sql

Is it possible to get last updated time and date of the row using MYSQL server.

Well there is no inbuild feature exists with MySQL. Though you can get the same effect by adding a timestamp column:
ALTER TABLE NAMEYOURTABLE
ADD COLUMN last_update TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
using above to create timestamp with name last_update column will make it pretty much automatically managed and updated. Now you can select from NAMEYOURTABLE the last updated row based on the timestamp.

Sqlite: CURRENT_TIMESTAMP is in GMT, not the timezone of the machine

I have a sqlite (v3) table with this column definition:
"timestamp" DATETIME DEFAULT CURRENT_TIMESTAMP
The server that this database lives on is in the CST time zone. When I insert into my table without including the timestamp column, sqlite automatically populates that field with the current timestamp in GMT, not CST.
Is there a way to modify my insert statement to force the stored timestamp to be in CST? On the other hand, it is probably better to store it in GMT (in case the database gets moved to a different timezone, for example), so is there a way I can modify my select SQL to convert the stored timestamp to CST when I extract it from the table?

I found on the sqlite documentation (https://www.sqlite.org/lang_datefunc.html) this text:
Compute the date and time given a unix
timestamp 1092941466, and compensate
for your local timezone.
SELECT datetime(1092941466, 'unixepoch', 'localtime');
That didn't look like it fit my needs, so I tried changing the "datetime" function around a bit, and wound up with this:
select datetime(timestamp, 'localtime')
That seems to work - is that the correct way to convert for your timezone, or is there a better way to do this?

simply use local time as the default:
CREATE TABLE whatever(
....
timestamp DATE DEFAULT (datetime('now','localtime')),
...
);

You should, as a rule, leave timestamps in the database in GMT, and only convert them to/from local time on input/output, when you can convert them to the user's (not server's) local timestamp.
It would be nice if you could do the following:
SELECT DATETIME(col, 'PDT')
...to output the timestamp for a user on Pacific Daylight Time. Unfortunately, that doesn't work. According to this SQLite tutorial, however (scroll down to "Other Date and Time Commands"), you can ask for the time, and then apply an offset (in hours) at the same time. So, if you do know the user's timezone offset, you're good.
Doesn't deal with daylight saving rules, though...

In the (admitted rare) case that a local datatime is wanted (I, for example, store local time in one of my database since all I care is what time in the day is was and I don't keep track of where I was in term of time zones...), you can define the column as
"timestamp" TEXT DEFAULT (strftime('%Y-%m-%dT%H:%M','now', 'localtime'))
The %Y-%m-%dT%H:%M part is of course optional; it is just how I like my time to be stored. [Also, if my impression is correct, there is no "DATETIME" datatype in sqlite, so it does not really matter whether TEXT or DATETIME is used as data type in column declaration.]

When having a column defined with "NOT NULL DEFAULT CURRENT_TIMESTAMP," inserted records will always get set with UTC/GMT time.
Here's what I did to avoid having to include the time in my INSERT/UPDATE statements:
--Create a table having a CURRENT_TIMESTAMP:
CREATE TABLE FOOBAR (
RECORD_NO INTEGER NOT NULL,
TO_STORE INTEGER,
UPC CHAR(30),
QTY DECIMAL(15,4),
EID CHAR(16),
RECORD_TIME NOT NULL DEFAULT CURRENT_TIMESTAMP)
--Create before update and after insert triggers:
CREATE TRIGGER UPDATE_FOOBAR BEFORE UPDATE ON FOOBAR
BEGIN
UPDATE FOOBAR SET record_time = datetime('now', 'localtime')
WHERE rowid = new.rowid;
END
CREATE TRIGGER INSERT_FOOBAR AFTER INSERT ON FOOBAR
BEGIN
UPDATE FOOBAR SET record_time = datetime('now', 'localtime')
WHERE rowid = new.rowid;
END
Test to see if it works...
--INSERT a couple records into the table:
INSERT INTO foobar (RECORD_NO, TO_STORE, UPC, PRICE, EID)
VALUES (0, 1, 'xyz1', 31, '777')
INSERT INTO foobar (RECORD_NO, TO_STORE, UPC, PRICE, EID)
VALUES (1, 1, 'xyz2', 32, '777')
--UPDATE one of the records:
UPDATE foobar SET price = 29 WHERE upc = 'xyz2'
--Check the results:
SELECT * FROM foobar
Hope that helps.

SELECT datetime(CURRENT_TIMESTAMP, 'localtime')

SELECT datetime('now', 'localtime');

Time ( 'now', 'localtime' ) and Date ( 'now', 'localtime' ) works.

You can also just convert the time column to a timestamp by using strftime():
SELECT strftime('%s', timestamp) as timestamp FROM ... ;
Gives you:
1454521888
'timestamp' table column can be a text field even, using the current_timestamp as DEFAULT.
Without strftime:
SELECT timestamp FROM ... ;
Gives you:
2016-02-03 17:51:28

I think this might help.
SELECT datetime(strftime('%s','now'), 'unixepoch', 'localtime');

The current time, in your machine's timezone:
select time(time(), 'localtime');
As per http://www.sqlite.org/lang_datefunc.html