Creating rows based on date range from another table

**Erland Sommarskog** · Aug 20 '06, 12:25 PM

Re: Creating rows based on date range from another table

rcamarda (robc390@hotmai l.com) writes:

I wish to build a table based on values from another table.
I need to populate a table between two dates from another table. Using
the START_DT and END_DT, create records between those dates.
I need a new column that is the days between the date and the MID_DT
The data I wish to end with would look something like this:
>
PERIOD DATE DAY_NO
200602 2005-07-06 -89
200602 2005-07-07 -88
200602 2005-07-08 -87
><...>
200602 2005-10-02 -2
200602 2005-10-03 -1
200602 2005-10-04 0
200602 2005-10-05 1
><...>
200602 2005-12-18 75
>
CREATE TABLE "dbo"."tblDates "
("PERIOD" CHAR(6) NOT NULL,
"START_DT" DATETIME NULL,
"MID_DT" DATETIME NULL,
"END_DT" DATETIME NOT NULL)
>
INSERT INTO tblDates VALUES('200505' ,2005-04-12,2005-07-05,2005-09-12)
INSERT INTO tblDates VALUES('200602' ,2005-07-06,2005-10-03,2005-12-18)
INSERT INTO tblDates VALUES('200603' ,2005-10-04,2006-01-17,2006-03-27)
INSERT INTO tblDates VALUES('200604' ,2006-01-18,2006-04-10,2006-06-19)
INSERT INTO tblDates VALUES('200605' ,2006-04-11,2006-07-04,2006-09-11)
INSERT INTO tblDates VALUES('200702' ,2006-07-05,2006-10-02,2006-12-18)

Thanks for posting table definition and data. However, I would appreciate
if you also tested your repro script before you post. I was puzzled not
getting any rows back first from my query, but then I realised that
2005-04-12 2005-09-12. (Run the above folliwed by a SELECT on the
table to see why.)

Anyway, as I said in another newsgroup, you need a table of numbers. Here
is a way to create such a table with a million numbers:

CREATE TABLE Numbers (Number int NOT NULL PRIMARY KEY);
WITH digits (d) AS (
SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION
SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION
SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION
SELECT 0)
INSERT Numbers (Number)
SELECT Number
FROM (SELECT i.d + ii.d * 10 + iii.d * 100 + iv.d * 1000 +
v.d * 10000 + vi.d * 100000 AS Number
FROM digits i
CROSS JOIN digits ii
CROSS JOIN digits iii
CROSS JOIN digits iv
CROSS JOIN digits v
CROSS JOIN digits vi) AS Numbers
WHERE Number 0

Given this table, we can write this query:

SELECT d.PERIOD, dateadd(DAY, n.Number - 1, d.START_DT),
datediff(DAY, d.MID_DT, dateadd(DAY, n.Number - 1, d.START_DT))
FROM tblDates d
CROSS JOIN Numbers n
WHERE dateadd(DAY, n.Number - 1, d.START_DT)
BETWEEN d.START_DT AND d.END_DT
ORDER BY d.PERIOD, 2

--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

**rcamarda** · Aug 20 '06, 03:05 PM

Re: Creating rows based on date range from another table

Erland,
Sorry about the insert, i see that its returning what I did not expect.
Originally I had the dates quoted, but sql bawked at that. I've been
trying to fix the insert, but after trying cast and convert, it still
wont go.
This gives error about conversion:
INSERT INTO tblDates VALUES ( '200602',cast(' 2005-07-06' AS
DATETIME),CAST( '2005-10-03' AS DATETIME), CAST('2005-12-18' AS
DATETIME))
AH! Finally got this to work:
INSERT INTO tblDates VALUES ('200505' ,convert(dateti me,
'2005-04-12'),convert(da tetime,'2005-07-05'),
convert(datetim e,'2005-09-12' ))

Im still trying to grasp the use of the numbers table. I have a D_Day
table that is the days from 1900 - 2100. Could that be used somehow?
(1900-01-01 has a surrogate key of 1 and 1900-01-02 is 2 and so forth)
You solution works, which I am appreciative of, tho it will take me
working with the code to figure out why :)
Thanks for teaching me something new!
Rob

Erland Sommarskog wrote:

rcamarda (robc390@hotmai l.com) writes:

I wish to build a table based on values from another table.
I need to populate a table between two dates from another table. Using
the START_DT and END_DT, create records between those dates.
I need a new column that is the days between the date and the MID_DT
The data I wish to end with would look something like this:

PERIOD DATE DAY_NO
200602 2005-07-06 -89
200602 2005-07-07 -88
200602 2005-07-08 -87
<...>
200602 2005-10-02 -2
200602 2005-10-03 -1
200602 2005-10-04 0
200602 2005-10-05 1
<...>
200602 2005-12-18 75

CREATE TABLE "dbo"."tblDates "
("PERIOD" CHAR(6) NOT NULL,
"START_DT" DATETIME NULL,
"MID_DT" DATETIME NULL,
"END_DT" DATETIME NOT NULL)

INSERT INTO tblDates VALUES('200505' ,2005-04-12,2005-07-05,2005-09-12)
INSERT INTO tblDates VALUES('200602' ,2005-07-06,2005-10-03,2005-12-18)
INSERT INTO tblDates VALUES('200603' ,2005-10-04,2006-01-17,2006-03-27)
INSERT INTO tblDates VALUES('200604' ,2006-01-18,2006-04-10,2006-06-19)
INSERT INTO tblDates VALUES('200605' ,2006-04-11,2006-07-04,2006-09-11)
INSERT INTO tblDates VALUES('200702' ,2006-07-05,2006-10-02,2006-12-18)

>
Thanks for posting table definition and data. However, I would appreciate
if you also tested your repro script before you post. I was puzzled not
getting any rows back first from my query, but then I realised that
2005-04-12 2005-09-12. (Run the above folliwed by a SELECT on the
table to see why.)
>
Anyway, as I said in another newsgroup, you need a table of numbers. Here
is a way to create such a table with a million numbers:
>
CREATE TABLE Numbers (Number int NOT NULL PRIMARY KEY);
WITH digits (d) AS (
SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION
SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION
SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION
SELECT 0)
INSERT Numbers (Number)
SELECT Number
FROM (SELECT i.d + ii.d * 10 + iii.d * 100 + iv.d * 1000 +
v.d * 10000 + vi.d * 100000 AS Number
FROM digits i
CROSS JOIN digits ii
CROSS JOIN digits iii
CROSS JOIN digits iv
CROSS JOIN digits v
CROSS JOIN digits vi) AS Numbers
WHERE Number 0
>
Given this table, we can write this query:
>
SELECT d.PERIOD, dateadd(DAY, n.Number - 1, d.START_DT),
datediff(DAY, d.MID_DT, dateadd(DAY, n.Number - 1, d.START_DT))
FROM tblDates d
CROSS JOIN Numbers n
WHERE dateadd(DAY, n.Number - 1, d.START_DT)
BETWEEN d.START_DT AND d.END_DT
ORDER BY d.PERIOD, 2
>
>
--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se
>
Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at
http://www.microsoft.com/sql/prodinf...ons/books.mspx

**Erland Sommarskog** · Aug 20 '06, 04:55 PM

Re: Creating rows based on date range from another table

rcamarda (robc390@hotmai l.com) writes:

Sorry about the insert, i see that its returning what I did not expect.
Originally I had the dates quoted, but sql bawked at that. I've been
trying to fix the insert, but after trying cast and convert, it still
wont go.
This gives error about conversion:
INSERT INTO tblDates VALUES ( '200602',cast(' 2005-07-06' AS

Yes, the above format could fail. There are three date formats in SQL
Server that are safe:

YYYYMMDD
YYYYMMDDTHH:MM: SS[.fff]
YYYY-MM-DDZ

Here T and Z stand for themselves.

Other formats are interpretated depending on DATEFORMAT and LANGUAGE
setting, and can fail or produced unexpected results if you don't know
what is going on.

Im still trying to grasp the use of the numbers table. I have a D_Day
table that is the days from 1900 - 2100. Could that be used somehow?
(1900-01-01 has a surrogate key of 1 and 1900-01-02 is 2 and so forth)

Yes, that dates table is essentially a table of numbers with a different
names. In fact, it appears that it has all the numbers as well!

I used a table of numbers, as numbers is the more general concept and
can be used in more places. But in fact, I added a table of dates to
our system before I added a table of numbers.

I leave it as an exercise to you how to use the dates table instead.
--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

**Ed Murphy** · Aug 21 '06, 06:45 AM

Re: Creating rows based on date range from another table

On Sun, 20 Aug 2006 12:38:11 +0000 (UTC), Erland Sommarskog
<esquel@sommars kog.sewrote:

>rcamarda (robc390@hotmai l.com) writes:

>I wish to build a table based on values from another table.
>I need to populate a table between two dates from another table. Using
>the START_DT and END_DT, create records between those dates.
>I need a new column that is the days between the date and the MID_DT
>The data I wish to end with would look something like this:
>>
>PERIOD DATE DAY_NO
>200602 2005-07-06 -89
>200602 2005-07-07 -88
>200602 2005-07-08 -87
>><...>
>200602 2005-10-02 -2
>200602 2005-10-03 -1
>200602 2005-10-04 0
>200602 2005-10-05 1
>><...>
>200602 2005-12-18 75

[snip]

>INSERT INTO tblDates VALUES('200602' ,2005-07-06,2005-10-03,2005-12-18)

>Anyway, as I said in another newsgroup, you need a table of numbers. Here
>is a way to create such a table with a million numbers:

What are the pros and cons of relying on such a table vs. using a
WHILE loop? Based on Rob's context of student registrations, let's
assume we're talking about a maximum of 300 iterations per row in
the original tblDates table.

**Erland Sommarskog** · Aug 21 '06, 07:55 AM

Re: Creating rows based on date range from another table

Ed Murphy (emurphy42@soca l.rr.com) writes:

What are the pros and cons of relying on such a table vs. using a
WHILE loop? Based on Rob's context of student registrations, let's
assume we're talking about a maximum of 300 iterations per row in
the original tblDates table.

The one risk with a table of numbers is that if you run of numbers, you
will get an incorrect result. That is one reason why I'm reluctant to
use it, if there are alternative solutions. But for a case like this,
when you need to fill up a space, a table of numbers - or dates - is what
you need.

A loop is more complex to program, and easier go wrong. And as a generic
solution, you face scalability problems.

--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

**Ed Murphy** · Aug 22 '06, 05:55 AM

Re: Creating rows based on date range from another table

On Mon, 21 Aug 2006 08:05:49 +0000 (UTC), Erland Sommarskog
<esquel@sommars kog.sewrote:

>Ed Murphy (emurphy42@soca l.rr.com) writes:

>What are the pros and cons of relying on such a table vs. using a
>WHILE loop? Based on Rob's context of student registrations, let's
>assume we're talking about a maximum of 300 iterations per row in
>the original tblDates table.

>
>The one risk with a table of numbers is that if you run of numbers, you
>will get an incorrect result. That is one reason why I'm reluctant to
>use it, if there are alternative solutions. But for a case like this,
>when you need to fill up a space, a table of numbers - or dates - is what
>you need.
>
>A loop is more complex to program, and easier go wrong.

I disagree, but then I have somewhat more experience with imperative
than functional programming. Consider:

x = first_date
while x <= last_date
insert x, datediff(x, mid_date) into <table>
x = dateadd(x, 1)
end while

versus

select dateadd(first_d ate, n), n - datediff(mid_da te, first_date)
into <table>
from numbers
where n between 0 and datediff(end_da te, first_date)

Okay, "where n between <limits>" makes sense as an analogue to a while
loop, but that stuff in line 1 looks like the stuff of headaches.

And as a generic
>solution, you face scalability problems.

I kind of figured. The query seems easy to get wrong, though, if
you're not familiar with the pattern; I first wrote it as "where
dateadd(first_d ate, n) between first_date and last_date", but that
seems like it'd be a good bit slower.

**Erland Sommarskog** · Aug 22 '06, 08:05 AM

Re: Creating rows based on date range from another table

Ed Murphy (emurphy42@soca l.rr.com) writes:

I disagree, but then I have somewhat more experience with imperative
than functional programming. Consider:
>
x = first_date
while x <= last_date
insert x, datediff(x, mid_date) into <table>
x = dateadd(x, 1)
end while
>
versus
>
select dateadd(first_d ate, n), n - datediff(mid_da te, first_date)
into <table>
from numbers
where n between 0 and datediff(end_da te, first_date)
>
Okay, "where n between <limits>" makes sense as an analogue to a while
loop, but that stuff in line 1 looks like the stuff of headaches.

Loops are particularly prone to two sorts of errors:

* They goes on forever, could be because of a sloppy mistake, of because the
logic is complicated.
* One-off errors because of incorrect loop conditions.

One-off errors are easy to make with set-based queries as well, but the
risk of infinite loops is nothing you have to lose sleep over.

--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

http://www.microsoft.com/sql/prodinfo/previousversions/books.mspx

Creating rows based on date range from another table

Creating rows based on date range from another table

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