How does the INTERSECT Function (DAX) work?

INTERSECT Function (DAX) compares two tables and find common rows. The INTERSECT function outputs a table with similar rows.

INTERSECT Formula Syntax

INTERSECT (<table_expression1>, <table_expression2>)

It returns the row intersection of two tables, retaining the duplicates.

Intersect is not commutative. That means, Intersect (T1, T2) can have a different result set than Intersect (T2, T1).
Duplicate rows are retained. That means, if a row appears in table_expression1 and table_expression2, it and all duplicates in table_expression_1 are included in the result set.
The column names will match the column names in table_expression1.
Columns are compared based on the positioning, and data comparison with no type coercion.
The returned table does not include columns from the tables related to table_expression1.

= SUMX (INTERSECT (SalesOldData,SalesNewData),[Sales Amount])