PostgreSQL unnest with empty array

Question

I use postgreSQL 9.1. In my database there is a table which looks like

id | ... | values
-----------------------
1  | ... | {1,2,3}
2  | ... | {}

Answer 1

Upon revisiting this question it struck me that this can be simpler and faster.
Reverse the logic of the currently accepted solution by @a_horse:

SELECT id, CASE WHEN values <> '{}' THEN unnest(values) END AS value
FROM   tbl

• This returns a row with NULL in value for an empty array as well as for a NULL array, because only an array with elements in it produces TRUE in the test values <> '{}'.

• Works for arrays of any type, since the literal '{}' is automatically coerced to a matching type.

• Without explicit ELSE branch, CASE returns NULL, which is what we want anyway.

• Arrays with a NULL elements will return rows regardless.
  However. I found an anomaly there and posted a question concerning that:

  • NULL emements lost when casting result of unnest()

  Turned out to be a bug that was fixed after my report for pg 9.3+.