Multiple choice technology databases

Consider this syntax MERGE INTO t1 USING t2 ON (join predicate) .... What does the MERGE syntax do ?

  1. It performs a merge join of the row from T2 only if it does'nt exist in the T1 table.

  2. It creates a natural join of table T1 and T2 for all columns that have the same name.

  3. It creates a Cartesian prodcut of table T1 and table T2 for all columns that have the same name.

  4. For each row from T2, it updates the row if it exists witin table T1, otherwise it inserts the row into T1.
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D Correct answer
Explanation

MERGE performs an upsert operation: for each row from the source (T2), it updates the target row if it exists in T1 based on the join condition, or inserts the row if it doesn't exist. MERGE is not a join type - it's a data manipulation command. It doesn't create natural joins or Cartesian products. The ON clause specifies the matching condition between source and target tables.

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