Seagate ST43401N/ND Información técnica descargar pdf (Pagina 76)

5-22 Implement: Making Required Application Changes

If Your Current Version is 4.x, 10.x, or 11.0.x Adaptive Server Enterprise 11.5

• Avoid mathematical manipulation of indexed columns when

using search arguments. For example, do not use mathematical

functions on the column itself, as shown in the example. Instead,

perform the function against the constant on the other side of the

operator.

Don’t:

select name from employee

where salary * 12 > 100000

Do:

select name

from employee

where monthly_salary > 100000 / 12

Avoid use of any function against the indexed column(s) on the

“left” side of the operator.

• Avoid incompatible datatypes in column names, search

arguments, or stored procedure parameters. Keep datatypes

consistent throughout an application or server. Incompatible

datatypes include:

- ﬂoat and integer

- char NOT NULL and varchar

- binary and varbinary

However, integer and intn (allows NULLs) are compatible

• Multiple

or clauses. or clauses are expensive for these reasons:

- If any portion of the

or clause requires a table scan, the whole

query will use table scanning.

or clausesrequire creating and sorting a work table

Consider using

unions as an alternative.

• Use

group by instead of using distinct without aggregates. This

reduces the size of the worktable created and, by storing distinct

values only in the

group by worktable, reduces the processing

resources needed to sort them.

Don’t:

select DISTINCT ship_to_address

from customer_orders

where last_order_date >= "01/01/1997"

Do:

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Seagate ST43401N/ND Información técnica Pagina 76