（单选题）
Consider this syntax： MERGE INTO t1 USING t2 ON （join predicate）….. What does the MERGE syntax do？（）
AIt performs a merge join of the row from T2 only if it doesn’t exist in the T1 table.
BIt creates a natural join of tables T1 and T2 for all columns that have the same name.
CIt creates a Cartesian product of table T1 and table T2 for all columns that have the same name.
DFor each row from T2, it updates the row if it exists within table T1, otherwise it inserts the row into T1.
正确答案
答案解析
略
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