How do I find some dates in SQL

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Hello All

I have a bunch of dates in a column in an SQL Server DB that looks like this

VB

There's a couple of questions that I have with SQL.
1. I'm trying to figure out how I can find 2014-03-11 if max day is 2014-03-13? Basically I'm trying to find the first day after there's been a break in dates.
2. Next I'm trying to do a count of the days that are NOT shown in this list
3. Lastly, is there a way to find a certain date in missing days. Example from '2014-03-13' find the 6th missing day that is not shown. (It should '2014-03-01')

I've got more questions but I'm pretty sure I'll figure it out from this.

Thanks

Mike

Posted 21-Mar-14 8:47am

mzrax

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4 solutions

Solution 2

This is a quite intriguing classic sql problem called "islands and gaps" (google it) with a whole load of solutions that keep growing.
I'll point you to one specific and good article[^] that should get you started. And you can come back here when you have more specific problems

Posted 21-Mar-14 10:16am

Jörgen Andersson

Comments

CHill60 23-Mar-14 6:40am

Nice link. 5'd

Jörgen Andersson 23-Mar-14 15:24pm

Thanks

Solution 1

This is not a complete answer to all your questions, because it is much simpler to do these in a general purpose language. Do you really need to answer in SQL-only?

Let's suppose so.
There are methods to generate a date range. So you can match the range with the dates you have to find the gaps. See: http://consultingblogs.emc.com/jamiethomson/archive/2007/01/11/T_2D00_SQL_3A00_-Generate-a-list-of-dates.aspx[^].

Posted 21-Mar-14 9:38am

Zoltán Zörgő

Solution 3

please read this hope some answer you can get

http://www.tutorialspoint.com/sql/sql-date-functions.htm[^]
http://technet.microsoft.com/en-us/library/ms186724.aspx[^]
http://publib.boulder.ibm.com/infocenter/iadthelp/v7r0/index.jsp?topic=/com.ibm.etools.iseries.langref2.doc/rbafzmstdatetimearith.htm[^]

Posted 23-Mar-14 0:07am

baliram bhande

Updated 23-Mar-14 0:08am

v2

Comments

mzrax 24-Mar-14 20:55pm

Thanks for the links they definitely have answered other questions that I had. I knew there was a page like the Microsoft link that you put but I could never find it.

Thanks

M

baliram bhande 25-Mar-14 6:03am

accept my ans if help my answer to u

baliram bhande 25-Mar-14 6:04am

Why down voted to me

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Maciej Los · Accepted Answer · 2014-03-23T06:55:00

Not sure what you want to achive, but have a look at example:

SQL

DECLARE @tmp TABLE (MyDate DATETIME)

INSERT INTO @tmp (MyDate)
VALUES ('2014-01-29'),
('2014-01-30'), ('2014-02-03'),
('2014-02-04'), ('2014-02-05'),
('2014-02-06'), ('2014-02-11'),
('2014-02-12'), ('2014-02-13'),
('2014-02-17'), ('2014-02-18'),
('2014-02-19'), ('2014-02-20'),
('2014-02-25'), ('2014-02-26'),
('2014-02-27'), ('2014-03-03'),
('2014-03-04'), ('2014-03-05'),
('2014-03-06'), ('2014-03-11'),
('2014-03-12'), ('2014-03-13')

SELECT t1.MyDate AS FirstDate, t2.MyDate AS SecondDate, DATEDIFF(d, t1.MyDate, t2.MyDate) AS DayDiff
FROM (
    SELECT ROW_NUMBER() OVER(ORDER BY MyDate) AS RowNo, MyDate
    FROM @tmp
    )
    AS t1
    INNER JOIN
    (
    SELECT ROW_NUMBER() OVER(ORDER BY MyDate) AS RowNo, MyDate
    FROM @tmp
    ) AS t2
    ON t1.RowNo = t2.RowNo-1

Result:

FirstDate               SecondDate              DayDiff
2014-01-29 00:00:00.000 2014-01-30 00:00:00.000 1
2014-01-30 00:00:00.000 2014-02-03 00:00:00.000 4
2014-02-03 00:00:00.000 2014-02-04 00:00:00.000 1
2014-02-04 00:00:00.000 2014-02-05 00:00:00.000 1
2014-02-05 00:00:00.000 2014-02-06 00:00:00.000 1
2014-02-06 00:00:00.000 2014-02-11 00:00:00.000 5
2014-02-11 00:00:00.000 2014-02-12 00:00:00.000 1
2014-02-12 00:00:00.000 2014-02-13 00:00:00.000 1
2014-02-13 00:00:00.000 2014-02-17 00:00:00.000 4
2014-02-17 00:00:00.000 2014-02-18 00:00:00.000 1
2014-02-18 00:00:00.000 2014-02-19 00:00:00.000 1
2014-02-19 00:00:00.000 2014-02-20 00:00:00.000 1
2014-02-20 00:00:00.000 2014-02-25 00:00:00.000 5
2014-02-25 00:00:00.000 2014-02-26 00:00:00.000 1
2014-02-26 00:00:00.000 2014-02-27 00:00:00.000 1
2014-02-27 00:00:00.000 2014-03-03 00:00:00.000 4
2014-03-03 00:00:00.000 2014-03-04 00:00:00.000 1
2014-03-04 00:00:00.000 2014-03-05 00:00:00.000 1
2014-03-05 00:00:00.000 2014-03-06 00:00:00.000 1
2014-03-06 00:00:00.000 2014-03-11 00:00:00.000 5
2014-03-11 00:00:00.000 2014-03-12 00:00:00.000 1
2014-03-12 00:00:00.000 2014-03-13 00:00:00.000 1

As you can see, you can compare dates by using Join. For further information, please see: Visual Representation of SQL Joins[^].
Using WHERE condition[^], you're able to filter your data to show dates where the distance between them is larger than 1 day:

SQL

WHERE DATEDIFF(d, t1.MyDate, t2.MyDate)>1

Try!