dynamic columns for dates - sql

Question

Columns [today], [30days ago], [60days ago], [90 days ago]
I have a table the will provide me with the sales number fro today and 30days ago, 60 days ago and 90 days ago,
But the issue I have is to figure out what the actual date was 60 days ago.
I wanted to update my script not show me 60days ago but to show me the actual date 60days ago. I want to make my columns dynamic so i get the actual date 90days ago.
Can anyone help me here?
Please remember this is a long scripts and 10 columns and I want to change each column to show me the actual date and not the 90 days ago.

Answer 1

You can use GETDATE() and DATEADD() to get these values:
SELECT CONVERT(DATE, GETDATE()) AS Today,
CONVERT(DATE, DATEADD(DAY, -30, GETDATE())) Minus30
Converting to DATE simply takes off the time portion.
Produces:
Today Minus30
2015-06-08 2015-05-09
To use these values you can assign a few variables and set the values to be used later in your code:
DECLARE #today DATE, #Minus30 DATE
SELECT #today = CONVERT(DATE, GETDATE()),
#Minus30 = CONVERT(DATE, DATEADD(DAY, -30, GETDATE()))
PRINT #today
PRINT #Minus30
To use the values as column names, you'll need to use some dynamic SQL:
DECLARE #today NVARCHAR(15), #Minus30 NVARCHAR(15)
SELECT #today = CONVERT(NVARCHAR(15), CONVERT(DATE, GETDATE())),
#Minus30 = CONVERT(NVARCHAR(15), CONVERT(DATE, DATEADD(DAY, -30, GETDATE())))
EXEC ('SELECT ''30'' AS ''' + #today + ''', ''123'' AS ''' + #Minus30 + '''')
Produces:
2015-06-08 2015-05-09
30 123

Answer 2

This is best handled in the client code that retrieves the sql results. Using c# as an example:
string sql = String.Format(
"SELECT [today] as [{0}], [30days ago] as [{1}], [60days ago] as [{2}], [90 days ago] as [{3}] FROM [MyTable]",
DateTime.Today.ToShortDateString(),
DateTime.Today.AddDays(-30).ToShortDateString(),
DateTime.Today.AddDays(-60).ToShortDateString(),
DateTime.Today.AddDays(-90).ToShortDateString());
If you really need to, you could put the same string logic into procedural sql, and save that to a stored procedure. But don't do that.

Answer 3

I haven't actually tried doing this, but you can try to use an sp_rename statement using the variable names that #Tanner suggested:
DECLARE #Minus30 DATE
SELECT #Minus30 = CONVERT(DATE, DATEADD(DAY, -30, GETDATE()))
EXEC sp_rename 'Table.[30days ago]', #Minus30, 'COLUMN'

Answer 4

If you are trying to build a list of dynamic date columns, you could do this using dynamic pivot method something like this:
Creating a Test Table
create table pvtTbl(DateColumns varchar(50),sales money,employeeid int);
insert into pvtTbl
select cast(getdate() as date) datecol,1249.00 as sales,123 employeeid
UNION
select cast(dateadd(day,-30,getdate()) as date) datecol,15615.00 as sales,456 employeeid
UNION
select cast(dateadd(day,-60,getdate()) as date) datecol,125583.00 sales,356 employeeid
UNION
select cast(dateadd(day,-90,getdate()) as date) datecol,25571.00 sales,859 employeeid
This part, I am just creating as an example to build the pivot table. But, you could actually create this step as an insert statement to a temp table in your stored proc, so that it will be updated each time to dynamically build your date columns using this query:
Query to build a list of needed date values
select cast(getdate() as date) datecol
UNION
select cast(dateadd(day,-30,getdate()) as date) datecol
UNION
select cast(dateadd(day,-60,getdate()) as date) datecol
UNION
select cast(dateadd(day,-90,getdate()) as date) datecol
After that, all you will need to do is build a dynamic pivot using STUFF function and XML path to first build a comma separated list of date values and then pivot it dynamically to output it as your columns like this:
Dynamic Pivot to build date columns
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
SET #cols = STUFF((SELECT distinct ',' + QUOTENAME(c.DateColumns)
FROM pvtTbl c
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT employeeid,' + #cols + ' from
(
select sales,employeeid,DateColumns
from pvtTbl
) x
pivot
(
sum(sales)
for DateColumns in (' + #cols + ')
) p '
execute(#query)
Anyway, this would be a good idea if you build this as a stored procedure. Let me know if you need any more help.
Demo