You are given a table, Functions, containing two columns: X and Y.
The Functions table is described as follows:
| Column | Type |
|---|---|
| X | Integer |
| Y | Integer |
Two pairs (X1, Y1) and (X2, Y2) are said to be symmetric pairs if X1 = Y2 and X2 = Y1.
Write a query to output all such symmetric pairs in ascending order by the value of X. List the rows such that X1 ≤ Y1.