I have a table in postgresql which stores time stamp with timezone for every row inserted.
How can I use postgresql's function to find a the difference in seconds from the timestamp in one of the rows already inserted to the current postgresql server time stamp?
Assuming that the column name is ts and the table name is t, you can query like this:
select current_timestamp - max(ts) from t;
If the table contains large amount of data, this query will be very slow. In that case, you should have index on the timestamp column.
Related
I created a function that retrieves data from multiple table and insert the result into a new table. I am passing few dates in the where clause to filter the applicable information. The dates are in timestamptz format. The query takes roughly a min to process. However when I make the change in the where clause to pass the date from another table, the query lags a lot. i.e.
My initial argument that doesn't lag is
where timestamp = '2022-01-05 04:00:00+00'
The lag is when I change this where clause to pass this date from another table.
where timestamp = select date_time from table_Test
The date_time in table_test is defined as timestamptz and the value is '2022-01-05 04:00:00+00'.
Any idea why the query lags when I pass the date argument from another table?
Thanks,
I have a postgres table "log", which has a column called "timestamp" which has the date and time of files in a folder.
I need to retrieve the latest timestamp from table and pass this in a "for condition" but initially the table will be empty, from second iteration i need to fetch from the table using pyspark
Please let me know how to go about it
so far i tried
log_qry = """select timestamp from log order by timestamp desc limit 1"""
cursor.execute = log_qry
conn.commit
this seems to be not working
Your query should be like below:
select timestamp from log order by timestamp desc limit 1
it will return 0 records if there is no record in your table log.
better you try it with max like below:
select max(timestamp) from log
it will return 1 record always, if table is empty then it will return null else it will return the max timestamp from the column timestamp.
Don't use reserve keywords and column name
timestamp is a reserved word and should be double-quoted if used as a name in a query.
If null is not acceptable for your "for condition" then coalesce it to a date/time very very long ago.
select coalesce(max("timestamp"), '0001-01-01T00:00:00'::timestamp) from "log";
I have been using postgreSQL. My table has 3 columns date, time and userId. I have to find out records between the given date and time frame. Since date and time columns are different, 'BETWEEN' clause is not providing valid results
Combine the two columns into a single timestamp by adding the time to the date:
select *
from some_table
where date_column + time_column
between timestamp '2017-06-14 17:30:00' and timestamp '2017-06-19 08:26:00';
Note that this will not use an index on date_column or time_column. You would need to create an index on that expression. Or better: use a single column defined as timestamp instead.
I want to copy records from one database to another using Pentaho. But I ran into a problem. Let's say there is a transaction_timestamp column ir Table1 with data type timestamp with time zone. But once I select records from the source DB and insert them into the other database - values of the column are offset by one hour or so. The weirdest thing - this doesn't even affect all records. I also tried something like this :
select
transaction_timestamp::timestamp without time zone as transaction_timestamp,
t1.* from
table1 t1
And it didn't work. Could the problem be that when I copy the records to the 2nd DB, it sets all values to the local timezone? But why then the select statement I mentioned doesn't work? And only a part of the records is affected?
I have a table in a PostgreSQL database with a column of TIMESTAMP WITHOUT TIME ZONE type. I need to order the records by this column and apparently PostgreSQL has some trouble doing it as both
...ORDER BY time_column
and
...ORDER BY time_column DESC
give me the same order of elements for my 3-element sample of records having the same time_column value, except the amount of milliseconds in it.
It seems that while sorting, it does not consider milliseconds in the value.
I am sure the milliseconds are in fact stored in the database because when I fetch the records, I can see them in my DateTime field.
When I first load all the records and then order them by the time_column in memory, the result is correct.
Am I missing some option to make the ordering behave correctly?
EDIT: I was apparently missing a lot. The problem was not in PostgreSQL, but in NHibernate stripping the milliseconds off the DateTime property.
It's a foolish notion that PostgreSQL wouldn't be able to sort timestamps correctly.
Run a quick test and rest asured:
CREATE TEMP TABLE t (x timestamp without time zone);
INSERT INTO t VALUES
('2012-03-01 23:34:19.879707')
,('2012-03-01 23:34:19.01386')
,('2012-03-01 23:34:19.738593');
SELECT x FROM t ORDER by x DESC;
SELECT x FROM t ORDER by x;
q.e.d.
Then try to find out, what's really happening in your query. If you can't, post a testcase and you will be helped presto pronto.
try cast your column to ::timestamp like that:
SELECT * FROM TABLE
ORDER BY time_column::timestamp