Seagate ST43401N/ND Información técnica descargar pdf (Pagina 72)

5-18 Implement: Making Required Application Changes

If Your Current Version is 4.x or 10.x Adaptive Server Enterprise 11.5

version 10.0 and is now obsolete. Applications that use it receive a

warning message and subqueries no longer return duplicates.

You may have used this option to obtain better performance. Because

of subquery processing changes, you must rewrite your query as a

join if you want duplicates. You should see better performance in

Adaptive Server for these types of queries.

union Limitations

Only 16 subqueries are allowed on one side of a

union. This does not

affect most queries because only 16 tables are allowed within one

query. This only affects a query with more than 16 subqueries where

some of those subqueries have no

from clauses.

Subqueries and NULL Results

Prior to SQL Server 11.x, a correlated expression subquery in the

set

clause of an update returned 0 instead of NULL when there were no

matching rows. SQL Server 11.x correctly returns NULL when there

are no matching rows, and raises an error.

For example, the following trigger tries to update a column that does

not permit NULL values:

update t1

set c1 = (select max(c1)

from inserted where t1.c2 = inserted.c2)

The correct trigger is:

update t1

set c1 = (select isnull(max(c1), 0)

from inserted

where t1.c2 = inserted.c2)

The where clause updates t1.c1 to 0, if the subquery does not return

any correlation values from the outer table t1.

No Subqueries in Updatable Cursors

The following constructs are no longer allowed in the

select statement

of updatable cursors:

• Subquery

•

distinct option

•

group by clause

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Seagate ST43401N/ND Información técnica Pagina 72