Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 11: Writing Scripts and Batches
key on another table (the parent). So what we have is a situation where the two child tables need to get
their key from the parent. Therefore, we need to insert a record into the parent first, and then retrieve the
identity value generated so we can make use of it in the other tables.
Try It Out Using @@IDENTITY
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Now that we have some tables to work with, we’re ready to try a little test script:
/*****************************************
** This script illustrates how the identity
** value gets lost as soon as another INSERT
** happens
****************************************** */
DECLARE @Ident int; -- This will be a holding variable
/* We’ll use it to show how we can
** move values from system functions
** into a safe place.
*/
INSERT INTO TestIdent
DEFAULT VALUES;
SET @Ident = @@IDENTITY;
PRINT ‘The value we got originally from @@IDENTITY was ‘ +
CONVERT(varchar(2),@Ident);
PRINT ‘The value currently in @@IDENTITY is ‘ + CONVERT(varchar(2),@@IDENTITY);
/* On this first INSERT using @@IDENTITY, we’re going to get lucky.
** We’ll get a proper value because there is nothing between our
** original INSERT and this one. You’ll see that on the INSERT that
** will follow after this one, we won’t be so lucky anymore. */
INSERT INTO TestChild1
VALUES
(@@IDENTITY);
PRINT ‘The value we got originally from @@IDENTITY was ‘ +
CONVERT(varchar(2),@Ident);
IF (SELECT @@IDENTITY) IS NULL
PRINT ‘The value currently in @@IDENTITY is NULL’;
ELSE
PRINT ‘The value currently in @@IDENTITY is ‘ + CONVERT(varchar(2),@@IDENTITY);
-- The next line is just a spacer for our print out
PRINT ‘’;
/* The next line is going to blow up because the one column in
** the table is the primary key, and primary keys can’t be set
** to NULL. @@IDENTITY will be NULL because we just issued an
** INSERT statement a few lines ago, and the table we did the
** INSERT into doesn’t have an identity field. Perhaps the biggest
** thing to note here is when @@IDENTITY changed - right after
** the next INSERT statement. */
INSERT INTO TestChild2
VALUES
(@@IDENTITY);