单项选择题

Considerthissyntax：MERGEINTOt1USINGt2ON（joinpredicate）…..WhatdoestheMERGEsyntaxdo？（）

A.ItperformsamergejoinoftherowfromT2onlyifitdoesn’texistintheT1table.
B.ItcreatesanaturaljoinoftablesT1andT2forallcolumnsthathavethesamename.
C.ItcreatesaCartesianproductoftableT1andtableT2forallcolumnsthathavethesamename.
D.ForeachrowfromT2,itupdatestherowifitexistswithintableT1,otherwiseitinsertstherowintoT1.

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