SQL Server 2012

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create table query_parts(id int identity, table_name varchar(100), col_name varchar(100), agg_func varchar(100), result decimal(12,6));
create table Table1 (Column_X int, Column_Y decimal(12,6))
insert into Table1
select 5, 5;
1 rows affected

insert into Table1
select 10, 10;
1 rows affected

insert into query_parts (table_name, col_name, agg_func)
select 'Table1', 'Column_X', 'Sum';
1 rows affected

insert into query_parts (table_name, col_name, agg_func)
select 'Table1', 'Column_Y', 'Avg';
1 rows affected

select * from query_parts;


id
table_name
col_name
agg_func
result


1
Table1
Column_X
Sum
null

2
Table1
Column_Y
Avg
null


select id, table_name, col_name, agg_func, 'select ' + agg_func + '(' + quotename(col_name) + ') from ' + quotename(table_name) + ';' as query
from query_parts


id
table_name
col_name
agg_func
query


1
Table1
Column_X
Sum
select Sum([Column_X]) from [Table1];

2
Table1
Column_Y
Avg
select Avg([Column_Y]) from [Table1];


declare @i int;
declare @query nvarchar(1000);

select @i = min(id) 
from query_parts;

while (@i is not null)
begin
  select @query = ('update query_parts set result = (' 
                   +  ('select ' + agg_func + '(' + quotename(col_name) + ') from ' + quotename(table_name))
                   + ') where id = ' + cast(@i as nvarchar))
  from query_parts
  where id = @i;
  
  exec sp_executesql @query;
  
  select @i = min(id) 
  from query_parts
  where id > @i;
end
2 rows affected

select * from query_parts;


id
table_name
col_name
agg_func
result


1
Table1
Column_X
Sum
15.000000

2
Table1
Column_Y
Avg
7.500000

id	table_name	col_name	agg_func	query
1	Table1	Column_X	Sum	select Sum([Column_X]) from [Table1];
2	Table1	Column_Y	Avg	select Avg([Column_Y]) from [Table1];