Seagate ST43401N/ND Technical Information Seite 71

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Migrating to Sybase Adaptive Server Enterprise 11.5 5-17
Adaptive Server Enterprise 11.5 If Your Current Version is 4.x or 10.x
Subquery Processing Changes
Changes in subquery processing are described in the following
sections:
Expression Subqueries 5-17
No set dup in subquery 5-17
union Limitations 5-18
Subqueries and NULL Results 5-18
No Subqueries in Updatable Cursors 5-18
Expression Subqueries
Expression subqueries may be slower in release 11.x than 10.x where:
The outer table is very large and has few duplicate correlation
values.
The inner table is small.
The subquery contains an aggregate.
The optimizer will not flatten this type of query to be processed as a
join. Such a query might look like this:
select * from huge_table where col_x=
(select sum(col_a) from tiny_table
where col_b = huge_table.col_y)
To get faster results, you can reformulate the query to mimic the
behavior of release 10.x, as demonstrated in this example:
select huge_table.col_y, s=sum(col_a)
into #t
from huge_table, tiny_table
where col_b=huge_table.col_y
group by huge_table.col_y
select huge_table.*
from huge_table, #t
where col_x=#t.s
and huge_table.col_y=#t.col_y
No set dup in subquery
The change in the
set dup in subquery command does not affect systems
being upgraded from 4.x, as this command was introduced in
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