IBM DB2: Generate list of dates between two dates - sql

Question

I need a query which will output a list of dates between two given dates.
For example, if my start date is 23/02/2016 and end date is 02/03/2016, I am expecting the following output:
Date
----
23/02/2016
24/02/2016
25/02/2016
26/02/2016
27/02/2016
28/02/2016
29/02/2016
01/03/2016
02/03/2016
Also, I need the above using SQL only (without the use of 'WITH' statement or tables). Please help.

Answer 1

I am using ,ostly DB2 for iSeries, so I will give you an SQL only solution that works on it. Currently I don't have an access to the server, so the query is not tested but it should work. EDIT Query is already tested and working
SELECT
d.min + num.n DAYS
FROM
-- create inline table with min max date
(VALUES(DATE('2015-02-28'), DATE('2016-03-01'))) AS d(min, max)
INNER JOIN
-- create inline table with numbers from 0 to 999
(
SELECT
n1.n + n10.n + n100.n AS n
FROM
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS n1(n)
CROSS JOIN
(VALUES(0),(10),(20),(30),(40),(50),(60),(70),(80),(90)) AS n10(n)
CROSS JOIN
(VALUES(0),(100),(200),(300),(400),(500),(600),(700),(800),(900)) AS n100(n)
) AS num
ON
d.min + num.n DAYS<= d.max
ORDER BY
num.n;
if you don't want to execute the query only once, you should consider creating a real table with values for the loop:
CREATE TABLE dummy_loop AS (
SELECT
n1.n + n10.n + n100.n AS n
FROM
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS n1(n)
CROSS JOIN
(VALUES(0),(10),(20),(30),(40),(50),(60),(70),(80),(90)) AS n10(n)
CROSS JOIN
(VALUES(0),(100),(200),(300),(400),(500),(600),(700),(800),(900)) AS n100(n)
) WITH DATA;
ALTER TABLE dummy_loop ADD PRIMARY KEY (dummy_loop.n);
It depends on the reason for which you like to use it, but you could even create table for lets say for 100 years. It will be only 100*365 = 36500 rows with just a date field, so the table will be quite small and fast for joins.
CREATE TABLE dummy_dates AS (
SELECT
DATE('1970-01-01') + (n1.n + n10.n + n100.n) DAYS AS date
FROM
(VALUES(0),(1),(2),(3),(4),(5),(6),(7),(8),(9)) AS n1(n)
CROSS JOIN
(VALUES(0),(10),(20),(30),(40),(50),(60),(70),(80),(90)) AS n10(n)
CROSS JOIN
(VALUES(0),(100),(200),(300),(400),(500),(600),(700),(800),(900)) AS n100(n)
) WITH DATA;
ALTER TABLE dummy_dates ADD PRIMARY KEY (dummy_dates.date);
And the select query could look like:
SELECT
*
FROM
dummy_days
WHERE
date BETWEEN(:startDate, :endDate);
EDIT 2: Thanks to #Lennart suggestion I have changed TABLE(VALUES(..,..,..)) to VALES(..,..,..) because as he said TABLE is a synonym to LATERAL that was a real surprise for me.
EDIT 3: Thanks to #godric7gt I have removed TIMESTAMPDIFF and will remove from all my scripts, because as it is said in the documentation:
These assumptions are used when converting the information in the second argument, which is a timestamp duration, to the interval type specified in the first argument. The returned estimate may vary by a number of days. For example, if the number of days (interval 16) is requested for the difference between '1997-03-01-00.00.00' and '1997-02-01-00.00.00', the result is 30. This is because the difference between the timestamps is 1 month, and the assumption of 30 days in a month applies.
It was a real surprise, because I was always trust this function for days difference.

Answer 2

For generating rows recusive SQL will needed.
Usually this looks like this in DB2:
with temp (date) as (
select date('23.02.2016') as date from sysibm.sysdummy1
union all
select date + 1 day from temp
where date < date('02.03.2016')
)
select * from temp
For whatever reason a CTE (using WITH) should be avoided.
A possible workaround would be setting
db2set DB2_COMPATIBILITY_VECTOR=8
which enables the use of the Oracle style recusion with CONNECT BY
SELECT date('22.02.2016') + level days as dt
FROM sysibm.sysdummy1 CONNECT BY date('22.02.2016') + level days <= date('02.03.2016')
Please note: after setting the DB2_COMPATIBILITY_VECTOR a instance restart is necessary.

Answer 3

This solution doesn't use WITH, but it does use WHILE and a temp table...hopefully that meets your needs still?
EDIT -- I built this in SSMS 2014
DECLARE #Start DATE
DECLARE #End DATE
SET #Start = '2016-02-23'
SET #End = '2016-03-02'
CREATE TABLE #Dates ([Date] DATE)
WHILE #Start <= #End
BEGIN
INSERT INTO #Dates
SELECT #Start
SET #Start = DATEADD(Day,1,#Start)
END
SELECT * FROM #Dates
DROP TABLE #Dates

Answer 4

I assume AS400 does not support recursive CTE's, and that's why you want a solution without them. I have no clue whether it supports any of the following constructions, but it might be worth a shot. First we will need a generator, any table with a sufficient number of rows will do. If you don't have a table large enough for the number of days you want you can create a cartesian product. Example:
select row_number() over ()
from a_table
cross join a_table
Another way of extending the domain is to create the powerset of a table using group by cube, see below.
Assume we one way or another can create a large enough set of rows. You can generate the dates like:
select date('23/02/2016') + n days
from (
select row_number() over () as n
from a_table
) as t
where n < 100
order by n
If for some reason you don't want to use an existing table, group by cube will produce a relation with a cardinality equal to the power set of the attributes. Here I use 4 columns which will generate 16 rows.
select date('2016-01-01') + row_number() over () days
from sysibm.dual x
group by cube(x.dummy, x.dummy, x.dummy, x.dummy)
If you want to generate say 100 rows you need 7 (since 2^7=128) attributes in the group by cube clause and a fetch first 100 rows:
select date('2016-01-01') + row_number() over () days
from sysibm.dual x
group by cube(x.dummy, x.dummy, x.dummy, x.dummy, x.dummy, x.dummy, x.dummy)
order by 1
fetch first 100 rows only