SAS Chapter 18: Modifying SAS Data Sets and Tracking Changes

1. Which type of integrity constraint would you place on the variable StoreID to ensure that there are no missing values and that there are no duplicate values?

UNIQUE

CHECK

PRIMARY KEY

NOT NULL

The PRIMARY KEY integrity constraint includes both the NOT NULL and UNIQUE constraints.

Explanation

The PRIMARY KEY integrity constraint includes both the NOT NULL and UNIQUE constraints.

2. Which code initiates generation data sets on the existing SAS data set Sasuser.Amounts and specifies that five historical versions are saved in addition to the base version?

Proc datasets lib=sasuser nolist; modify Amounts (genmax=6);quit;

Proc datasets lib=sasuser nolist; modify Amounts (genmax=5);quit;

Proc datasets lib=sasuser nolist; modify Amounts (gennum=6);quit;

Proc datasets lib=sasuser nolist; modify Amounts (gennum=5);quit;

You use the DATASETS procedure and the MODIFY statement to specify a number of generation data sets for a data set. The GENMAX= option is used to specify the number of versions to save. The number you specify includes the base version.

Explanation

You use the DATASETS procedure and the MODIFY statement to specify a number of generation data sets for a data set. The GENMAX= option is used to specify the number of versions to save. The number you specify includes the base version.

3. Which of the following statements about audit trails is true?

They record information about changes to observations in a data set each time the data set is replaced.

They record information about changes to observations in a data set each time the data is modified in place.

Audit trails are used to track changes that are made to a data set in place.

Explanation

Audit trails are used to track changes that are made to a data set in place.

4. Which code deletes all generations of the data set Sasuser.Amounts including the base data set?

Proc datasets lib=sasuser nolist; delete amounts (gennum=ALL);quit;

Proc datasets lib=sasuser nolist; delete amounts (gennum=HIST);quit;

Proc datasets lib=sasuser nolist; delete amounts (gennum=0);quit;

Proc datasets lib=sasuser nolist; delete amounts;quit;

The keyword ALL is used to indicate that you want to delete all generations of the specified data set including the base version. The keyword HIST deletes the generation data sets, but saves the base version.

Explanation

The keyword ALL is used to indicate that you want to delete all generations of the specified data set including the base version. The keyword HIST deletes the generation data sets, but saves the base version.

5. The automatic variable _IORC_ is created when you use the MODIFY statement with a BY statement or the KEY= option. How can you use the value of _IORC_?

To determine whether the index specified on the KEY= option is a valid index

To determine the number of observations that were updated in the master data set

To determine the status of the I/O operation

To determine the number of observations that could not be updated in the master data set

The value of _IORC_ is a numeric return code that indicates the status of the most recently executed I/O operation. Checking the value of this variable allows you to detect abnormal I/O conditions and direct execution in particular ways.

Explanation

The value of _IORC_ is a numeric return code that indicates the status of the most recently executed I/O operation. Checking the value of this variable allows you to detect abnormal I/O conditions and direct execution in particular ways.

6. Which DATA step uses the transaction data set Records.Overnight to update the master data set Records.Snowfall by accumAmt?

Data records.snowfall; modify records.snowfall records.overnight key=accumAmt;run;

Data records.snowfall; modify records.overnight records.snowfall; by accumAmt;run;

Data records.snowfall; modify records.snowfall records.overnight; by accumAmt;run;

Data records.snowfall; modify records.snowfall records.overnight; update accumAmt;run;

In the MODIFY statement, you specify the master data set followed by the transaction data set. Then you specify the variable in the BY statement.

Explanation

In the MODIFY statement, you specify the master data set followed by the transaction data set. Then you specify the variable in the BY statement.

7. Which statement about using the MODIFY statement in a DATA step is true?

You cannot modify the descriptor portion of the data set using the MODIFY statement.

You can use the MODIFY statement to change the name of a variable.

The MODIFY statement in a DATA step can be used only to modify the values in a data set. It cannot be used to modify the descriptor portion of the data set.

Explanation

The MODIFY statement in a DATA step can be used only to modify the values in a data set. It cannot be used to modify the descriptor portion of the data set.

8. Which statement about using the KEY= option in the MODIFY statement is true?

The KEY= option is used to specify a variable to match for updating observations.

The index named in the KEY= option must be a simple index.

When you use the KEY= option, you must specify the update that you want to make to the data set.

Explanation

When you use the KEY= option, you must specify the update that you want to make to the data set.

9. Which code creates an audit trail on the SAS data set Reports.Quarter1?

Proc datasets nolist; audit quarter1; initiate;quit;

Proc datasets lib=reports nolist; audit initiate reports.quarter1;quit;

Proc datasets lib=reports nolist; initiate audit quarter1;quit;

Proc datasets lib=reports nolist; audit quarter1; initiate;quit;

To initiate an audit on an existing SAS data set with the DATASETS procedure, you specify the data set in the AUDIT statement, and then you specify the INITIATE statement. You specify the library with the LIB= option.

Explanation

To initiate an audit on an existing SAS data set with the DATASETS procedure, you specify the data set in the AUDIT statement, and then you specify the INITIATE statement. You specify the library with the LIB= option.

10. Which PROC DATASETS step creates an integrity constraint named val_age on the data set Survey to ensure that values of the variableage are greater than or equal to 18?

Proc datasets nolist; modify age; ic create val_age=check(where=(age>=18));quit;

Proc datasets nolist; modify Survey; ic create val_age=check(age>=18);quit;

Proc datasets nolist; modify survey; ic create val_age=check(where=(age>=18));quit;

In the MODIFY statement, you list the SAS data set that you want to modify. Then you use the IC CREATE statement to create the integrity constraint. This integrity constraint is a CHECK constraint and you use a WHERE clause to specify the condition that the variable values must meet.

Explanation

In the MODIFY statement, you list the SAS data set that you want to modify. Then you use the IC CREATE statement to create the integrity constraint. This integrity constraint is a CHECK constraint and you use a WHERE clause to specify the condition that the variable values must meet.

SAS Chapter 18: Modifying SAS Data Sets And Tracking Changes