单项选择题 The ST_INFO master table has millions of rows that are updated very rarely. It has a STATE_CODE column that contains the value for 25 states. The table is frequently queried on the STATE_CODE column.  Which type of index would you suggest to improve the query performance？（）

多项选择题 AconstraintinatableisdefinedwiththeINITIALLYIMMEDIATEclause.YouexecutedtheALTERTABLEcommandwiththeENABLEVALIDATEoptiontoenabletheconstraintthatwasdisabled.Whatarethetwoeffectsofthiscommand？（）

单项选择题 Your database is started by using the server parameter file （SPFILE）. You issued this command to change the value of the LOG_BUFFER initialization parameter：  ALTER SYSTEM SET LOG_BUFFER=24M SCOPE=BOTH  What would be the outcome of this command？（）