How to find the first and last occurrences of a specific character inside a string in PostgreSQL

Question

I want to find the first and the last occurrences of a specific character inside a string. As an example, consider a string named \"2010-####-3434\", and suppose the charact

Answer 1

9.5+ with array_positions

Using basic PostgreSQL array functions we call string_to_array(), and then feed that to array_positions() like this array_positions(string_to_array(str,null), c)

SELECT
  arrpos[array_lower(arrpos,1)] AS first,
  arrpos[array_upper(arrpos,1)] AS last
FROM ( VALUES
  ('2010-####-3434', '#')
) AS t(str,c)
CROSS JOIN LATERAL array_positions(string_to_array(str,null), c)
  AS arrpos;