The LIBNAME Statement for Relational Databases

CAST= LIBNAME Option

Specifies whether SAS or the Teradata DBMS server performs data conversions.

Default value:	none
Valid in:	SAS/ACCESS LIBNAME statement
DBMS support:	Teradata

Syntax
Syntax Description
Details
Examples
See Also

Syntax

CAST=YES | NO

Syntax Description

YES: forces data conversions (casting) to be done on the Teradata DBMS server and overrides any data overhead percentage limit.
NO: forces data conversions to be done by SAS and overrides any data overhead percentage limit.

Details

Internally, SAS numbers and dates are floating-point values. Teradata has varying 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 point (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. This is especially true when 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.

The following Teradata types are candidates for casting:

INTEGER
BYTEINT
SMALLINT
DECIMAL
DATE

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, then 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 the 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.

CAST= only applies when you are reading Teradata tables into SAS. It does not apply when you are writing Teradata tables from SAS.

Also, CAST= only applies to SQL that SAS generates for you. If you supply your own SQL with the explicit SQL feature of PROC SQL, you must code your own casting clauses to force data conversions to occur in Teradata instead of SAS.

Examples

The following example demonstrates the use of the CAST= option in a LIBNAME statement to force casting for all tables referenced:

libname mydblib teradata user=testuser pw=testpass cast=yes;
proc print data=mydblib.emp;
where empno<1000;
run;

proc print data=mydblib.sal;
where salary>50000;
run;

The following example demonstrates the use of the CAST= option in a table reference in order to turn off casting for that table:

proc print data=mydblib.emp (cast=no);
where empno<1000;
run;