Create Date Records

I need to read dates in a table and then create more dates depending on the difference between todays date and date in the record.
Let's say todays date is 2015-10-23.

Table A

2015-10-23
2015-10-26
2015-11-06

If the difference between todays date and the Table A date = 0 do nothing.
The difference between todays date and the second record is 3, so, I need to insert the following records into this table :
 2015-10-25
 2015-10-24
 2015-10-23
The difference between todays date and the second record is 14, so, I need to insert the following records into this table :
2015-11-05
2015-11-04
All the way to 2015-10-23

Having duplicate dates in the table is no problem. I am going to use this table in a IN statement.
thayduckProgrammer AnalystAsked:
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Jim HornMicrosoft SQL Server Developer, Architect, and AuthorCommented:
A WHILE loop would work here.   Something like <air code>
Declare @dt_end date = CAST(GETDATE() as date) 
Declare @dt_start = ??? FROM TableA WHERE ?? 
Declare @i int = 0

WHILE @i <= DATEDIFF(day, @dt_start, @dt_end) 
   begin
   INSERT INTO ?? (??) VALUES(DATEADD(day, @i, @dt_start)) 
   SET @i = @i + 1
   end

Open in new window


You could also create a SQL Server Calendar Table of days, then this would be a simple matter of...
INSERT INTO ?? (??)
SELECT PKDate
FROM days
WHERE PKDate >= @dt_start AND PKDate <= @dt_end

Open in new window

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Scott PletcherSenior DBACommented:
A "standard" tally table, just a table of sequential numbers, is great for this.  I can't post in-line tally table code myself (filter at work blocks it, thinking it is "sql injection"[!]), but you can find the code on-line to create a tally_table using CTEs:

--WITH (code to create tally_table of sequential numbers from 1 to, say, 10,000)
--INSERT INTO ... ( ... )
SELECT DATEADD(DAY, t.number, a.date_column) --, ...
FROM [Table A] a
INNER JOIN tally_table t ON t.number BETWEEN 1 AND DATEDIFF(DAY, GETDATE(), a.date_column)
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Scott PletcherSenior DBACommented:
My code to create the tally table is here; this code loads the tally table with 0 thru 1,000,000:

http://www.experts-exchange.com/questions/28697468/Sql-Extract-Between-Parentheses.html#a40883940
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PortletPaulfreelancerCommented:
>>"Having duplicate dates in the table is no problem. I am going to use this table in a IN statement."

That sounds like an approach that might have better options. While generating rows for "missing dates" is quite straight forward, I would prefer to understand what you are actually going to do with them.
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thayduckProgrammer AnalystAuthor Commented:
Here is what I did after reading Scott's post on 10/23/2015:

-- Create EscalationDates temp table
      IF Object_id(N'tempdb..#EscalationDates', N'U') IS NOT NULL
        DROP TABLE #EscalationDates

      -- Create temp table
      CREATE TABLE #EscalationDates
        (
           EscalationDates CHAR (10)
        )

      --Write date records that are <= to the latest date that the user can choose from Escalation Days dropdown        
      --Right now, the latest date is 'Next 14 Days', so I will create date records in the TallyDates table that represent the next 14 days from today.
      --If today is 10/05/2015, then I will create date records of 10/05/2015 thru 10/19/2015 in this table.
      --Will use this table later to determine which Note table records to keep.
   
    ;  WITH TallyDates
           AS (SELECT tDate = Dateadd(DAY, 14, CONVERT(DATE, Getdate())) --latest date user can choose from dropdown        
               UNION ALL
               SELECT tDate = Dateadd(DAY, -1, tDate) --create records that are less then the latest date user can choose from the dropdown    
               FROM   TallyDates
               WHERE  tDate > CONVERT(DATE, Getdate())) -- Stop writing records when you have reached todays date
               

      --Write records into the #EscalationDates table that represent what the user actually chose from the Escalation Days dropdown.
      --If user chose chose Today, then only put in record from TallyTable that has todays date.
      --If user chose chose Tomorrow, then only put in record from TallyTable that has tomorrows date.
      --If user chose chose Next 7 Days, then only put in records from TallyTable that represent next 7 days from today.
      --If user chose chose Next 14 Days, then only put in records from TallyTable that represent next 14 days from today.

      INSERT INTO #EscalationDates
      SELECT [tDate]
      FROM   TallyDates
             INNER JOIN #EscalationDays
                     ON EscalationCode >= tDate
      WHERE  ( EscalationCode = tDate
               AND EscalationCode = CONVERT(DATE, Getdate()) )
              OR ( EscalationCode = tDate
                   AND EscalationCode = Dateadd(DAY, +1, CONVERT(DATE, Getdate())) )
              OR ( EscalationCode >= tDate
                   AND EscalationCode <> CONVERT(DATE, Getdate())
                   AND EscalationCode <> Dateadd(DAY, +1, CONVERT(DATE, Getdate())) )

Some of the code I found poking around the internet then changed it to work for me.
Some is Scott's.

Now, after building my SQL Notes table from a Oracle a table, I will delete any record in the Notes table that does not have a date that is contained in #EscalationDates table.

I am pretty sure the way I am doing this can be improved, but the final outcome is doing what I need it to do.
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thayduckProgrammer AnalystAuthor Commented:
Thanks, your suggestions got me going in the right direction to solve my issue.
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