string_to_array ( string text, delimiter text [, null_string text ] ) → text[]Splits the
string at occurrences of delimiter and forms the resulting fields into a text array. If delimiter is NULL, each character in the string will become a separate element in the array. If delimiter is an empty string, then the string is treated as a single field. If null_string is supplied and is not NULL, fields matching that string are replaced by NULL. See also array_to_string.string_to_array('xx~~yy~~zz', '~~', 'yy') → {xx,NULL,zz}