Merge and append queries

Merge adds columns

Merge matches key columns between two tables and brings related data side by side. The join kind decides which matched or unmatched rows survive, and the result usually contains a nested table column that you expand.

Append adds rows

Append concatenates table rows and aligns fields by column name. It is a natural fit for monthly, regional, or channel tables with the same logical schema.

Think in table shape

Merge makes a table wider by matching keys and adding related columns. Append makes a table longer by stacking rows and aligning columns by name.

For merge questions, also inspect which unmatched rows must survive because that determines the join kind. For append questions, inspect whether the input tables represent the same kind of rows.

Exam clue: side by side = merge. Stacked vertically = append.