Example 1: provide default values for all columns
+-----+-----+---------------+---------------+---+-------------+-------------+
| Row | idx | auxdata_1.idx | auxdata_2.idx | x | auxdata_1.y | auxdata_2.z | 
+-----+-----+---------------+---------------+---+-------------+-------------+
| 0   | 1   | 1             | 1             | 1 | 4           | 6           | 
+-----+-----+---------------+---------------+---+-------------+-------------+
| 1   | 2   | 2             | -2147483648   | 2 | 5           | -2147483648 | 
+-----+-----+---------------+---------------+---+-------------+-------------+
| 2   | 3   | -2147483648   | 3             | 3 | -2147483648 | 7           | 
+-----+-----+---------------+---------------+---+-------------+-------------+
Example 2: skip the entry only when the first auxiliary tree does not match
+-----+-----+---------------+---------------+---+-------------+-------------+
| Row | idx | auxdata_1.idx | auxdata_2.idx | x | auxdata_1.y | auxdata_2.z | 
+-----+-----+---------------+---------------+---+-------------+-------------+
| 0   | 1   | 1             | 1             | 1 | 4           | 6           | 
+-----+-----+---------------+---------------+---+-------------+-------------+
| 1   | 2   | 2             | -2147483648   | 2 | 5           | -2147483648 | 
+-----+-----+---------------+---------------+---+-------------+-------------+
Example 3: keep entries from the main tree for which there is no match in the auxiliary tree
+-----+-----+---+
| Row | idx | x | 
+-----+-----+---+
| 2   | 3   | 3 | 
+-----+-----+---+