Creating a loop script in SQL - sql

Question

I have been asked to create a loop script in SQL which will pull table name, column name and an operation from a list which I will create. Then loop through each row in the list and create a query. See below my thinking.
Table 1, Column x, Sum;
Table 2, Column z, Sum;
Table 3, Column F, Sum;
Loop
Select operation(ColumnName)
From TableName
End Loop (When there is nothing left in the list)
Am I going along the correct path with this or am I going wrong somewhere? Or is it even possible?
Any help you can offer will be really appreciated

Answer 1

DECLARE #ToSquare INT
DECLARE #Square INT
SET #ToSquare = 0
WHILE #ToSquare < 100
BEGIN
SET #ToSquare = #ToSquare + 1
SET #Square = #ToSquare * #ToSquare
IF #Square > 1000
BREAK
PRINT #Square
END

Answer 2

I think you can using CURSOR.
Some thing like this:
DECLARE #your_Cursor CURSOR
SET #your_Cursor = CURSOR FAST_FORWARD
FOR SELECT ColumnName FROM TableName
OPEN #your_Cursor
FETCH NEXT FROM #your_Cursor
INTO #value
WHILE ##FETCH_STATUS = 0 BEGIN
-- do something
END
CLOSE #your_Cursor
DEALLOCATE #your_Cursor

Answer 3

You don't really need a loop, you can use a simple select statement to generate the queries, for example:
Demo on DB Fiddle
create table query_parts(table_name varchar(100), col_name varchar(100), agg_func varchar(100));
insert into query_parts
select 'Table1', 'Column X', 'Sum';
insert into query_parts
select 'Table2', 'Column Y', 'Avg';
select 'select ' + agg_func + '(' + quotename(col_name) + ') from ' + quotename(table_name) + ';' as query
from query_parts
UPDATE
If you also want to execute the queries, you can use the following example to get started:
Demo on DB Fiddle
create table query_parts(id int identity, table_name varchar(100), col_name varchar(100), agg_func varchar(100), result decimal(12,6));
insert into query_parts (table_name, col_name, agg_func)
select 'Table1', 'Column_X', 'Sum';
insert into query_parts (table_name, col_name, agg_func)
select 'Table1', 'Column_Y', 'Avg';
create table Table1 (Column_X int, Column_Y decimal(12,6))
insert into Table1
select 5, 5;
insert into Table1
select 10, 10;
Loop through the query_parts table and execute queries:
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