Answer is C "Use of bitmap indexes" B also dependent on also need SQL_COMPAT='NPS' https://www.ibm.com/docs/en/db2/11.1?topic=nps-double-dot-notation https://www.ibm.com/docs/en/db2/11.1?topic=oracle-implicit-casting-character-graphic-constants

Correct answer is C: Bitmapped Indexes DB2 optimizer will create bitmap indexes dynamically when they are needed. This removes the requirement having to create and maintain static bitmap indexes. For example, you may create a bitmap index on a low cardinality column in Oracle, bit in DB2 this will be done for you. With static bitmap indexes there is an additional overhead in that each insert, update and delete needs to update the indexes. Dynamic bitmap indexes have no disk or update overhead and DB2 can give you good performance by accessing the index and handling the ROWIDS in memory.

Sorry answer is B as C also need SQL_COMPAT='NPS'

Question says which will be on without setting the variables, so Implicit casting, DUAL need DB2_COMPATIBILITY_VECTOR to be either 100 or ORA So the answer should be B and C

The question is very ambiguous. The answers B and D can be correct ! IF you use SQL_COMPAT, you can activate NPS compatibility features as "Double-dot notation". If you user DB2_COMPATIBILITY_VECTOR registry variabke, you can use "DUAL table" compatibility feature. Reference : DB2_COMPATIBILITY_VECTOR : https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.apdv.porting.doc/doc/r0052867.html SQL_COMPAT : https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.apdv.porting.doc/doc/c_compat_nz.html