The following documentation comment has been logged on the website:
Page: https://www.postgresql.org/docs/9.5/queries-order.html
Description:
In https://www.postgresql.org/docs/9.5/queries-order.html it is said that
the following is intentionally not allowed:
```
SELECT a + b AS sum, c FROM table1 ORDER BY sum + c; -- wrong
```
It took me a while to figure out how to do it properly so I propose to add
the following (or similar) info:
---
If you need to sort by this kind of expression, you will have to retrieve an
extra column with the required computation and use it as a sorting key:
```
SELECT a + b AS sum, c FROM table1, a + b + c AS my sorting_key ORDER BY
my_sorting_key; -- correct
```