How to Dynamically Generate Columns in SQL to Count Customer Rewards?
Jan 09, 2025 pm 03:21 PM
Dynamicly create columns in SQL
Dynamic columns
The task includes generating dynamic columns in SQL to display the reward count for each customer type.
Table structure and data
We have the following forms:
- Customer (customer ID, name)
- Customer Rewards (Type ID, Description)
- Reward (reward ID, type ID, customer ID)
Demand
The goal is to create columns for each reward type and display the reward count per customer per column, along with a total row.
Solution
1. Use PIVOT with known number of columns
For a fixed number of columns, you can use the PIVOT function:
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;
2. PIVOT using dynamic SQL
For an unknown number of columns, use dynamic SQL:
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)
Total Row
To include a total row, use ROLLUP:
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
Conclusion
The above solution allows you to dynamically generate columns based on the types available and display the rewards count per column for each customer, including a total row.
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