Internally, SAS numbers
and dates are floating-point values. Teradata has several formats
for numbers, including integers, floating-point values, and decimal
values. Number conversion must occur when you are reading Teradata
numbers that are not floating points (Teradata FLOAT).
SAS/ACCESS
can use the Teradata CAST= function to cause Teradata to perform numeric
conversions. The parallelism of Teradata makes it suitable for performing
this work, particularly if you are running SAS on
z/OS, where CPU
activity can be costly.
CAST= can cause more
data to be transferred from Teradata to SAS, as a result of the option
forcing the Teradata type into a larger SAS type. For example, the
CAST= transfer of a Teradata BYTEINT to SAS floating point adds seven
overhead bytes to each row transferred.
These Teradata types
are candidates for casting:
SAS/ACCESS limits data
expansion for CAST= to 20% to trade rapid data conversion by Teradata
for extra data transmission. If casting does not exceed a 20% data
increase, all candidate columns are cast. If the increase exceeds
this limit, SAS attempts to cast Teradata DECIMAL types only. If casting
only DECIMAL types still exceeds the increase limit, data conversions
are done by SAS.
You can alter the casting
rules by using either CAST= or CAST_OVERHEAD_MAXPERCENT= LIBNAME option.
With CAST_OVERHEAD_MAXPERCENT=, you can change the 20% overhead limit.
With CAST=, you can override the percentage rules:
-
CAST=YES forces Teradata to cast
all candidate columns.
-
CAST=NO cancels all Teradata casting.