Which two statements are true about the tuning of PL/SQL code? (Choose two.)
A.
Redundant SQL statements in PL/SQL code should be avoided.
B.
Implicit data type conversion in PL/SQL code can improve performance.
C.
Usage of the NOT NULL constraint in PL/SQL code can degrade performance.
D.
If you have one PL/SQL program unit instead of multiple smaller executable sections,
performance can be improved.
AC
A. true
B. false
Minimize Implicit Data Type Conversion
For example, convert NUMBER values to PLS_INTEGER values and then use the PLS_INTEGER values in expressions.
PLS_INTEGER operations use hardware arithmetic, so they are faster than NUMBER operations, which use library arithmetic.
http://docs.oracle.com/cloud/latest/db121/LNPLS/tuning.htm#BCGGGIBD
Implicit and Explicit Data Conversion
Implicit data type conversion can have a negative impact on performance, especially if the data
type of a column value is converted to that of a constant rather than the other way around.
If implicit data type conversion occurs in an index expression, then Oracle Database might not
use the index because it is defined for the pre-conversion data type.
This can have a negative impact on performance.
http://docs.oracle.com/cloud/latest/db121/SQLRF/sql_elements002.htm#SQLRF30027
C. true
Unnecessary NOT NULL Constraints
In PL/SQL, using the NOT NULL constraint incurs a performance cost.
http://docs.oracle.com/cd/B10501_01/appdev.920/a96624/12_tune.htm