SAS Adv 12月真题63题.doc

1. When attempting to minimize memory usage, the most efficient way to do group processing when using the MEANS procedure is to use: A. the BY statement. B. GROUPBY with the NOTSORTED specification. C. the CLASS statement. D. multiple WHERE statements. (The question is pretty clear-cut, IMO. It alludes to the standard long- bearded practical trick used in the situation when MEANS/SUMMARY with CLASS uses too much memory. It does not ask what is more efficient in general (which would be to use something else instead of MEANS if possible), just what leads to the minimal memory footprint, and the answer is A. (Answer B is just a distraction - a common device in computer-adaptive tests). The reason is that without BY, MEANS creates and builds its AVL tree for the entire file and all categorical values crossings found in CLASS. With BY, the proc builds the tree for the current BY group only, computes the stats, then erases the tree before the next BY group starts, creates and builds it again, and so on. The erase/create process is not a zero cost one, so the smaller the more numerous the BY groups are, the more it slows does the processing; however, the smaller is the largest BY group, the smaller is the memory footprint.) 2. The SAS data set WORK.CHECK has a variable named Id_Code in it. Which SQL statement would create an index on this variable? A. create index Id_Code on WORK.CHECK; B. create index(Id_Code) on WORK.CHECK; C. make index=Id_Code from WORK.CHECK; D.define index(Id_Code) in WORK.CHECK; 3. Given the SAS data sets: WORK.EMPLOYEE WORK.NEWEMPLOYEE Name Dept Names Salary Alan Sales Michelle 50000 Michelle Sales Paresh 60000 A SAS program is submitted and the following is written to the SAS log: 101 proc sql; 102 select dept, name 103 from WORK.EMPLOYEE 104