Merge vs. Append

Append

Preferable to have the same columns. If the same columns are not present, extra columns will be added for the source that does not have the column and it will be populated with null values.

Append stacks the rows on top of each other.
For example, two sources with 12 and 15 records would create a table of 27 records.

Duplicates are not removed.

Merge

Merge is equivalent of a SQL join. It is based on joining rows.

If joining two sources each having two columns, consisting of a common key and a value, the output of a standard left outer join would have three to four columns (depending if the key is repeated). The number of rows would be the same as the first table.

Six join types are supported.

Criteria for the join are required.