Consider this syntax： MERGE INTO t1 USING t2 ON （join predicate）….. What does the MERGE syntax do？（） ["It performs a merge join of the row from T2 only if it doesn’t exist in the T1 table. ","It creates a natural join of tables T1 and T2 for all columns that have the same name. ","It creates a Cartesian product of table T1 and table T2 for all columns that have the same name. ","For each row from T2, it updates the row if it exists within table T1, otherwise it inserts the row into T1."]
在外界的作用下，直流电动机电枢外加电压和感应电动势的极性相同的这种工作状态称为（） ["反接制动状态","反馈制动状态","能耗制动状态","加速状态"]
项目
未再生加氢催化剂卸剂的有哪些主要的安全基本技术要求？
User defined locale files can be stored in which two locations?（） ["DRAM","SDRAM","CME flash，slot0","CUE flash，slot0","TFTP directory specified by cnf-file location command"]
消费者被侵害权益后有哪些救济途径？
