DB2- select rows with date_column of last month - db2

I need to select count(field) from table where the date_column is within the last month, i.e. from the first of the last month till the first of this month. As this query will be automated it will need to refer to the last month of any given day.
Also the date_column has a datatype of timestamp
Thanks in advance!


SELECT (CAST(current timestamp AS DATE)) - (DAY(CAST(current timestamp AS DATE)) - 1)DAYS FROM sysibm.sysdummy1;
SELECT (CAST(current timestamp AS DATE)) - (DAY(CAST(current timestamp AS DATE)) - 1)DAYS
- 1 MONTH
FROM sysibm.sysdummy1;
Managed to find these queries, to find the first of this month and last month

Related

Finding the last date of the previous quarter from current date in PostgreSQL

For example: If my current date is 2022-07-21, my query should give me 2022-06-30.
I could easily do it in IBM DB2 but struggling in postgresql.

You can truncate the current date to its quarter, then remove 1 day from that (and potentially cast back to date):
-- You really only need the last column, the other two just show the different steps in the process
SELECT DATE_TRUNC('quarter', CURRENT_DATE)
, DATE_TRUNC('quarter', CURRENT_DATE) - '1 day'::INTERVAL
, (DATE_TRUNC('quarter', CURRENT_DATE) - '1 day'::INTERVAL)::DATE
outputs
+---------------------------------+---------------------------------+----------+
|date_trunc |?column? |date |
+---------------------------------+---------------------------------+----------+
|2022-07-01 00:00:00.000000 +00:00|2022-06-30 00:00:00.000000 +00:00|2022-06-30|
+---------------------------------+---------------------------------+----------+

How to get records from table which has timestamp starting from particular date of previous month to particular date of this month in postgres?

I have a customer_visit table, my requirement is to get the records of previous month starting from 3rd date to current month 2nd date and which contains flag 'Y'. How can I achieve this in Postgres. Following is the sample of my table. Any help is appreciated.

Use make_date() function from postgres to construct the date and query on it.
select * from customer_visit
where created_time > make_date(2018, date_part('month', now())::int - 1, 03)
and created_time <= make_date(2018, date_part('month', now())::int, 02)
and flag = 'Y';
You can use date_part('year', timestamp) to extract year also from current date.

Subtract month from date column

I would like to subtract one month from a date column in Amazon Redshift (a fork of PostgreSQL 8.0.2).
So for each date column in a table, it will add another column date_minus_a_month.
I tried this code
Select date,date::date -interval '1 month'
from table
and received an error:
Interval values with month or year parts are not supported.
Does anyone have a solution for this?

You can use datesub, although I just use dateadd for everything and use negative numbers.
eg
SELECT getdate() as right_now, dateadd(month, -1, getdate()) as last_month
Docs: https://docs.aws.amazon.com/redshift/latest/dg/r_DATEADD_function.html

Getting a weird result for ISO Date in Postgresql

I have a table task_details. I need to select its weekly date from this table. I have used ISO Year & ISO Week to extract the weekly dates from this table as I want to extract its week number as 53 if its Dec,2015 then on the days 28 Dec,29 Dec,30 Dec,31 Dec and 1 Jan '16,2 Jan '16 since it should not separate to two different weeks for these sort of dates. The query I have used for ISO Year & ISO Week is given below.
select
name, id,
to_date(week || ' ' || yr, 'IW IYYY') week_date,
sum(worked_hours) worked_hours_per_week,
week, yr
from (
select
name, id,
newdate, hours worked_hours,
to_number(to_char(newdate, 'IW'), '99') week,
extract( year from newdate) yr
from task_details t
) sub
where worked_hours > 0
group by name, id, to_date(week || ' ' || yr, 'IW IYYY'), week, yr
order by yr, week
It is working fine for the weeks but then I am getting this weird result for one date for a record in the table. The table doesn't have the data for the year 2017.Also, the yr column is showing 2016 which is as desired but then the newdate column and week column is giving weird result. Why is this happening? How do I fix this ?
Here is the SQL fiddle for it :http://sqlfiddle.com/#!15/53abf/1

You should not mix week with year in the extract function as year is for the Gregorian calendar rather than the special ISO calendar.
See section 9.9.1 and comments about week.
to_number(to_char(newdate, 'IW'), '99') is effectively extract(week from newdate)
Changing the yr column to be extract(isoyear from newdate) solves your problem.
Adjusted SQL Fiddle

#gwaigh already cleared up your confusion of Gregorian and ISO year.
However, your query would be simpler and faster with date_trunc() to get the first day of each week:
SELECT name, id
, date_trunc('week', newdate)::date AS week_date
, extract(week FROM newdate)::int AS week
, extract(isoyear from newdate)::int AS isoyr -- must be ISO year to match
, sum(hours) AS worked_hours_per_week
FROM task_details
WHERE hours > 0
GROUP BY name, id, week_date, week, yr
ORDER BY week_date;
Also simplified your query.
SQL Fiddle.
Either way, if you work with timestamptz then year, week or date depend on your current timezone setting. (It can be a different year, depending on where you are right now.)

How to get current month and Last month in Redshift

I am wondering if I can get last month and current month in Redshift? I looked at functions at http://docs.aws.amazon.com/redshift/latest/dg/r_CURRENT_DATE_TIME_functions.html
For current month, I guess I can do the following:
LEFT(CURRENT_DATE, 7)
For previous month, I came up with the following:
LEFT(ADD_MONTHS(CURRENT_DATE, -1), 7)
But I am wondering if there is a simpler way of doing these?

SELECT EXTRACT(month FROM CURRENT_DATE);
SELECT EXTRACT(month FROM CURRENT_DATE - '1 month'::interval);