Using Local Variable Value As Query Criteria SQL Server - sql

Question

Background: I want to compare each column in all tables for two Person records by looping through all possible columns. I then want to run a common table expression which uses each column as it loops, and if the second Person column is NULL, I want it to update with the value of the first Person column, for all duplicate records based on specific criteria.
This will essentially loop through all duplicates and update them to match, prior to deleting one.
I am running a stored procedure which loops through table columns. I would like to use those columns in a query. Here is what I have:
declare table_columns cursor local dynamic for
select BaseTable,
DBColumn
from viewTableInfo
declare #BaseTable nvarchar (100)
declare #DBColumn nvarchar (100)
open table_columns
while (1 = 1)
begin
fetch next from table_columns into #BaseTable, #DBColumn
if (##FETCH_STATUS <> 0 ) break
;with CTE as
(
select firstName,
lastName,
#DBColumn AS Column,
rn = ROW_NUMBER()OVER(PARTITION BY firstName, lastName ORDER BY pID)
from Person p
inner join Company c ON c.pID = p.pID -- joined because variable may be column from Company table.
where p.pID in (1, 2)
)
select destinationProperty = case
when c1.Column = c2.Column then c2.Column
when c2.Column IS NULL THEN c1.Column
ELSE c2.Column END
from cte c1
inner join cte c2 on c1.firstName = c2.firstName and c1.lastName = c2.LastName and c2.rn = c1.rn + 1
When I run this, I get zero records in the result set because the common table expression is selecting the value of the variable #DBColumn, which, for each loop, is the actual Column Name.
What I need is to be able to use the actual Column name in the query and get the value of that column for each pID in the result set.
Is this possible?

Answer 1

Not sure of exact requirement to use cursor and dynamic column names here, but you can get the required functionality using dynamic SQL.
Changed the loop not to use 1=1 , instead to check for cursor status.
declare table_columns cursor local dynamic for
select BaseTable,
DBColumn
from viewTableInfo
declare #BaseTable nvarchar (100)
declare #DBColumn nvarchar (100)
declare #query nvarchar(max)
open table_columns
fetch next from table_columns into #BaseTable, #DBColumn
WHILE ##FETCH_STATUS = 0
begin
set #query =';with CTE as
(
select firstName,
lastName,
' + #DBColumn + ' AS Column,
rn = ROW_NUMBER()OVER(PARTITION BY firstName, lastName ORDER BY pID)
from Person p
inner join Company c ON c.pID = p.pID -- joined because variable may be column from Company table.
where p.pID in (1, 2)
)
select destinationProperty = case
when c1.Column = c2.Column then c2.Column
when c2.Column IS NULL THEN c1.Column
ELSE c2.Column END
from cte c1
inner join cte c2 on c1.firstName = c2.firstName and c1.lastName = c2.LastName and c2.rn = c1.rn + 1'
exec sp_executesql #query
fetch next from table_columns into #BaseTable, #DBColumn
end