Returns the union of the tables whose columns match.
A table that will participate in the union.
A table that contains all the rows from each of the table expressions.
The tables must have the same number of columns.
Columns are combined by position in their respective tables.
The column names in the return table will match the column names in the first Table.
Duplicate rows are retained.
The returned table has lineage where possible. For example, if the first column of each Table has lineage to the same base column C1 in the model, the first column in the UNION result will have lineage to C1. However, if combined columns have lineage to different base columns, or if there is an extension column, the resulting column in UNION will have no lineage.
When data types differ, the resulting data type is determined based on the rules for data type coercion.
The returned table will not contain columns from related tables. Therefore, when the result corresponds to a base table, once applied to the filter context it does not involve the expanded table and it only filters columns of he base table.
Other related functions are:
Contributors: Alberto Ferrari, Marco Russo
MSDN documentation: https://docs.microsoft.com/en-us/dax/union-function-dax