How to increment column ordinal position in a while function? - sql

Question

Abstract: I have a table with multiple columns and I am trying to implement a while (loop) function to all the columns to pull out the average of each column.
I coded this to attribute a number to each column (to ease the possibility of an incremental method)
Declare #tablename as varchar(128)
Declare #column1 as varchar(128)
Delect #tablename = 'MOMENTUM_Results'
Select #column1 = sc.name
from sysobjects as so inner join syscolumns as sc on so.id = sc.id
where so.name = #tablename and sc.colid = 2
When I print this code it prints the name of the column based on the number I put from 1 to 122.
Code for the loop function:
WHILE ....
BEGIN
SET #SQL = 'SELECT AVG(MR.[' + #column1 + ']) From MOMENTUM_Quintile MQ
Left Join MOMENTUM_Returns MR on MQ.Mnemonic = MR.Mnemonic WHERE MQ.[' + #column1 + '] = 1'
END
But I definitely do not have a clue how to integrate this function into the loop so the function goes through all the columns one by one, therefore looking for some advice..
Thank you!
R.H.

Answer 1

Can you not just move your SELECT from sys.Columns into the body of your WHILE loop to get the one you're after? Something like this...
DECLARE #TABLENAME AS VARCHAR(128);
DECLARE #COLUMN1 AS VARCHAR(128);
DECLARE #COUNTER INT;
SET #TABLENAME = 'MOMENTUM_Results';
SET #COUNTER = 1;
WHILE ....
BEGIN
SELECT #COLUMN1 = C.Name
FROM sys.Columns C
WHERE OBJECT_NAME(C.object_id) = #TABLENAME
AND C.column_id = #COUNTER
;
SET #SQL = 'SELECT AVG(MR.[' + #COLUMN1 + ']) From MOMENTUM_Quintile MQ
Left Join MOMENTUM_Returns MR on MQ.Mnemonic = MR.Mnemonic WHERE MQ.[' + #COLUMN1 + '] = 1';
... Other Stuff ...
SET #COUNTER = #COUNTER + 1;
END
;
Maybe I didn't properly understand your question, but if you already have everything written out you could just change the placement to select the column names you want.
Of course you can also add additional conditions to make sure you're getting matched columns, or columns by name, or whatever...
EDIT:
You asked about inserting the resultant query into a table. If you already have a table with a column ready to receive the query, then the answer is simple... In the body of your WHILE loop, after retrieving the desired query, simply add an INSERT command:
WHILE ....
BEGIN
SELECT #COLUMN1 = C.Name
FROM sys.Columns C
WHERE OBJECT_NAME(C.object_id) = #TABLENAME
AND C.column_id = #COUNTER
;
SET #SQL = 'SELECT AVG(MR.[' + #COLUMN1 + ']) From MOMENTUM_Quintile MQ
Left Join MOMENTUM_Returns MR on MQ.Mnemonic = MR.Mnemonic WHERE MQ.[' + #COLUMN1 + '] = 1';
INSERT INTO <mytable> (<querycolumn>) VALUES (#SQL);
... Other Stuff ...
SET #COUNTER = #COUNTER + 1;
If you need to create the table, you can do that in the head of the script, before declaring anything else, and do the same thing during the WHILE:
DECLARE #TABLENAME AS VARCHAR(128);
DECLARE #COLUMN1 AS VARCHAR(128);
DECLARE #COUNTER INT;
SET #TABLENAME = 'MOMENTUM_Results';
SET #COUNTER = 1;
CREATE TABLE <mytable> (<optional_column1>,<optional_column2>,<querycolumn>);
....
WHILE ....
BEGIN
SELECT #COLUMN1 = C.Name
FROM sys.Columns C
WHERE OBJECT_NAME(C.object_id) = #TABLENAME
AND C.column_id = #COUNTER
;
SET #SQL = 'SELECT AVG(MR.[' + #COLUMN1 + ']) From MOMENTUM_Quintile MQ
Left Join MOMENTUM_Returns MR on MQ.Mnemonic = MR.Mnemonic WHERE MQ.[' + #COLUMN1 + '] = 1';
INSERT INTO <mytable> (<querycolumn>) VALUES (#SQL);
... Other Stuff ...
SET #COUNTER = #COUNTER + 1;

Answer 2

First get all the column names in that table into a temporary table(#temp)
Get the count of all columns(#count_of_columns) in that temptable.
declare a variable #count=1
Declare while loop as While(#count<=#count_of_columns)
--> fetch the column name one after another inside this while loop using the following query
SET #column1=(select top 1 column1 from
(select Row_number()over (order by column1) as r_n_n, column1
from #temp) aa
where r_n_n >=#Count)
--> use your actual code here
--> increment the #count variable
set #count = #count + 1

Answer 3

Don't use loops or cursors, if you can avoid them. The devil of procedural thinking is pulling you away from the light of set based approaches deep into pain and misery!
I know the column names in advance, I just did it to ease the way I would loop through each column
NO! This is not easing the way but punishing the poor engine :-)
Is it this you are looking for?
CREATE TABLE dbo.Test(ID INT, VAl1 DECIMAL(14,4), Val2 DECIMAL(14,4), Val3 DECIMAL(14,4));
GO
INSERT INTO dbo.Test VALUES(1,1,10,100),(2,2,20,200),(3,3,30,300);
GO
SELECT AVG(Val1) AS Avg1,AVG(Val2) AS Avg2,AVG(Val3) AS Avg3
FROM dbo.Test;
GO
DROP TABLE dbo.Test;
The result
Avg1 Avg2 Avg3
2.000000 20.000000 200.000000
UPDATE
If you just want to be lazy and avoid typing, you might try something like this:
SELECT ',AVG(' + COLUMN_NAME + ') AS ' + QUOTENAME('AVG_' + COLUMN_NAME)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA='dbo' AND TABLE_NAME='Test'
FOR XML PATH('')
The result
,AVG(ID) AS [AVG_ID],AVG(VAl1) AS [AVG_VAl1],AVG(Val2) AS [AVG_Val2],AVG(Val3) AS [AVG_Val3]
With this trick you can build your hard coded statement quite easily :-)