Help for Trigger

Hello

I would like to get the content of a field based in the field Name.
Suppose a table with a field Named 'LastName' for wich there is a trigger
after update
I store the field name in a local variable

Set @.ColName = 'LastName'

How can I retrieve the value of the @.ColName from the inserted table using
the @.Colname variable ?

I tried this:

Set @.Cmd = 'DECLARE @.DataValue varchar(100) Set @.DataValue = (Select i.' +
@.ColName + ' from inserted i) print @.DataValue'
exec (@.Cmd)

print @.Cmd gives

DECLARE @.DataValue varchar(100) Set @.DataValue = (Select i.LastName from
inserted i) print @.DataValue

But I got the following error

Server: Msg 208, Level 16, State 1, Line 1
Invalid object name 'inserted'.

Any idea why ?

Thanks for your help

ThierryOn Fri, 23 Apr 2004 20:57:10 +0200, Thierry Marneffe wrote:

>Hello
>I would like to get the content of a field based in the field Name.
>Suppose a table with a field Named 'LastName' for wich there is a trigger
>after update
>I store the field name in a local variable
>Set @.ColName = 'LastName'
>How can I retrieve the value of the @.ColName from the inserted table using
>the @.Colname variable ?
>I tried this:
>Set @.Cmd = 'DECLARE @.DataValue varchar(100) Set @.DataValue = (Select i.' +
>@.ColName + ' from inserted i) print @.DataValue'
>exec (@.Cmd)
>print @.Cmd gives
>DECLARE @.DataValue varchar(100) Set @.DataValue = (Select i.LastName from
>inserted i) print @.DataValue
>But I got the following error
>Server: Msg 208, Level 16, State 1, Line 1
>Invalid object name 'inserted'.
>Any idea why ?
>Thanks for your help
>Thierry

Hi Thierry,

The inserted and deleted pseudo-tables can only be used in the
trigger. Invoking dynamic SQL creates a new environment, so you can't
use the inserted and deleted tables there.

If you don't use dynamic SQL, all will be swell:

CREATE TRIGGER TestIt
ON MyTable AFTER UPDATE
AS
DECLARE @.DataValue varchar(100)
SET @.DataValue =
(SELECT LastName
FROM inserted)
PRINT @.DataValue
go

Of course, this trigger will still result in an error if you perform
an update that affects more than one row - always remember that a
trigger is fired exactly once for each update statement, regardless of
the number of rows that match the search criteria (can be anything
from 0 up to the complete table) and regardless of whether the data
was actually chaged or not (ie UPDATE MyTable SET MyColumn = MyColumn
will fire the trigger and will have the complete table in the inserted
ande deleted pseudo-tables).

Best, Hugo
--

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