| re: Help for Trigger
On Fri, 23 Apr 2004 20:57:10 +0200, Thierry Marneffe wrote:
[color=blue]
>
>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[/color]
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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