Dynamically create columns sql

Question

I have a table of Customers

Customer ID        Name         
   1               John        
   2               Lewis        
   3               Mary

I have another table CustomerRewards

 TypeID           Description
   1                Bronze
   2                Silver
   3                Gold
   4               Platinum
   5               AnotherOne

And the final table

 RewardID          TypeID          CustomerID
    1                1                 1
    2                1                 1
    3                2                 1
    4                2                 2

The customerTypes table is dynamic, many of these types can be added and removed. Basically all I want is the columns to be generated dynamically and a count in each, something like

CustomerName        Bronze        Silver     Gold      Platinum     AnotherOne    total
   John               2             1         0           0             0           3
   Lewis              0             1         0           0             0           1
 Grand TOTAL          2             2         0           0             0           4

The problem like I said it that the types are dynamic and the customers are dynamic so I need the columns to be dynamic depending on the types in the system

I have tagged c# as I need this in a DataGridView

Thanks in advance

This looks like a pivot. I've done a few, but I can't type one up from memory. Maybe a a view in the DB created from pivoting the data on the SQL side? — Doug Dawson
– Doug Dawson, Commented Sep 28, 2012 at 15:43
You probably want dynamic pivot, if you need to do this in SQL. See, e.g., simple-talk.com/blogs/2007/09/14/… But that's not really a clean solution. If you can wait to get your data into C#, you could use LINQ to do this. — Kris Harper
– Kris Harper, Commented Sep 28, 2012 at 15:43
These do look complex! thanks for the comments, I will look into Pivot but if anyone has an easy solution please feel free — CR41G14
– CR41G14, Commented Sep 28, 2012 at 15:50

Taryn · Accepted Answer · 2013-05-22 14:16:29Z

You will want to use a PIVOT function for this. If you have a known number of columns, then you can hard-code the values:

select name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
from
(
  select c.name,
    cr.description,
    r.typeid
  from customers c
  left join rewards r
    on c.id = r.customerid
  left join customerrewards cr
    on r.typeid = cr.typeid
) x
pivot
(
  count(typeid)
  for description in ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
) p;

See SQL Fiddle with Demo.

Now if you have an unknown number of columns, then you can use dynamic SQL to PIVOT:

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT ',' + QUOTENAME(description) 
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT name,' + @cols + ' from 
             (
                select c.name,
                  cr.description,
                  r.typeid
                from customers c
                left join rewards r
                  on c.id = r.customerid
                left join customerrewards cr
                  on r.typeid = cr.typeid
            ) x
            pivot 
            (
                count(typeid)
                for description in (' + @cols + ')
            ) p '

execute(@query)

See SQL Fiddle With Demo

If you need to include the Total column, then you can use ROLLUP (Static Version Demo):

select name, sum([Bronze]) Bronze, sum([Silver]) Silver, 
  sum([Gold]) Gold, sum([Platinum]) Platinum, sum([AnotherOne]) AnotherOne
from 
(
  select name, [Bronze], [Silver], [Gold], [Platinum], [AnotherOne]
  from
  (
    select c.name,
      cr.description,
      r.typeid
    from customers c
    left join rewards r
      on c.id = r.customerid
    left join customerrewards cr
      on r.typeid = cr.typeid
  ) x
  pivot
  (
    count(typeid)
    for description in ([Bronze], [Silver], [Gold], [Platinum], [AnotherOne])
  ) p
) x
group by name with rollup

Dynamic version (Demo):

DECLARE @cols AS NVARCHAR(MAX),
    @colsRollup AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX)

select @cols = STUFF((SELECT ',' + QUOTENAME(description) 
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

select @colsRollup 
      = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ QUOTENAME(description)
                    from customerrewards
                    group by description, typeid
                    order by typeid
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')


set @query 
          = 'SELECT name, '+ @colsRollup + '
             FROM
             (
                SELECT name,' + @cols + ' from 
                 (
                    select c.name,
                      cr.description,
                      r.typeid
                    from customers c
                    left join rewards r
                      on c.id = r.customerid
                    left join customerrewards cr
                      on r.typeid = cr.typeid
                ) x
                pivot 
                (
                    count(typeid)
                    for description in (' + @cols + ')
                ) p 
              ) x1
              GROUP BY name with ROLLUP'

execute(@query)

You have one SQL Injection flaw / usability bug: = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ description Should be: = STUFF((SELECT ', Sum(' + QUOTENAME(description) + ') as '+ QUOTENAME(description) Otherwise, that is an awesome post!
@shellster Yup, you are right. I updated my code. Thanks for catching that.

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