Using variable for UPDATE() the checker if the column is Updated or not

Question

Is it possible to use a variable in UPDATE() which check if a column is updated or not?

here is my sample code:

DECLARE @ColumnCount int
DECLARE @ColumnC         


        

Answer 1

A few things: You may want to handle the first time through the loop because the name would not have changed the first time through. You may want to handle when @ColumnName is null because that would mean your query did not return a row although your query below should always return a value.

DECLARE @ColumnCount INT 
DECLARE @ColumnCounter INT 
DECLARE @ColumnName NVARCHAR(max) 
DECLARE @temp varchar(max)

SET @ColumnCounter = 0 

SELECT @ColumnCount = Count(c.column_name) 
FROM   information_schema.columns c 
WHERE  c.table_name = 'Province' 

WHILE @ColumnCount >= @ColumnCounter 
  BEGIN 
      SET @ColumnName = NULL 

      SELECT @ColumnName = c.column_name 
      FROM   information_schema.columns c 
      WHERE  c.table_name = 'Province' 
             AND c.ordinal_position = @ColumnCounter 

      IF ( @ColumnName != @temp ) 
        BEGIN 
        --do something 
        END
      SET @temp = @ColumnName
      SET @ColumnCounter = @ColumnCounter + 1 
  END 

Answer 2

to check for column is actually updated in after update trigger you can use deleted and inserted special tables msdn in which trigger code can find old and new versions of rows of updating table

remember that it is possible to find there more than 1 row in each table. for example you execute update table1 set col1 = value1 where some_condition in trigger number of rows affects by some_condition, will be presented in inserted and deleted tables

to find out in trigger in what rows some column is actual updating, you can join inserted and deleted tables on some primary key and compare values of this column

the update() function takes as parameter column name not a sting variable with name as value

for example using update() in triggers check this update(some_column) is true when some_column present in update set statement, even value of column not changing.

it seems like you can not write universal trigger to count number of columns updated, if you need that count you need to manually write trigger for each table with somethig like this

declare @count int = 0
if update(col1) set @count = @count + 1
if update(col2) set @count = @count + 1
...