Why would you use the following FLASHBACK TABLE command？（） FLASHBACK TABLE emp TO TIMESTAMP （’11：45’，’hh12：mi’）; ["to undo the changes made to the EMP table since the specified time","to restore the EMP table that was wrongly dropped from the database","to view the transactions that have modified the EMP table since the specified time","to view the changes made to the EMP table for one or more rows since the specified time","to recover the EMP table to a point in time in the past by restoring the most recent backu"]
Which two statements about subqueries are true? （） [" A single row subquery can retrieve data from only one table."," A SQL query statement cannot display data from table B that is referred to in its subquery, unless table B is included in the main query's FROM clause."," A SQL query statement can display data from table B that is referred to in its subquery, without including B in its own FROM clause."," A single row subquery can retrieve data from more than one table."," A single row subquery cannot be used in a condition where the LIKE operator is used for comparison."," A multiple-row subquery cannot be used in an INSERT statement to insert multiple rows at a time."]
请写出插花作品的六种常见造型。
所用骨料的不同，划分的混凝土类别不包括（） ["水泥混凝土","矿渣混凝土","碎石混凝土","卵石混凝土"]
Your database is running in ARCHIVELOG mode,and the database is open. You execute an RMAN backup and specify the KEEP clause.Which components are backed up when this option is specified?（） [" only the control file, the current SPFILE, and data files"," only the current SPFILE and data files if autobackup is disabled"," only the data files and the archived redo logs"," the control file, current SPFILE file, data files, and archived redo log"]
简述数据电文的原件规制。
