Postgres 16

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create table test ( word text );

CREATE TABLE


insert into test values (''), ('  '), ('value'), (null), ('  not blank  ');

INSERT 0 5


create function replace_blanks(text, text) returns text
immutable
as $$
  select coalesce(regexp_replace($1, '^\s*$', $2), $2)
$$ language sql;

CREATE FUNCTION


select
  '"' || word || '"',
  case 
  when trim(word) = '' then 'default' 
  else coalesce(word, 'default') 
  end as word_case,
  coalesce(regexp_replace(word, '^\s*$', 'default'), 'default') as word_coalesce,
  replace_blanks(word, 'default') as word_function
from test;


?column?
word_case
word_coalesce
word_function


""
default
default
default

"  "
default
default
default

"value"
value
value
value

null
default
default
default

"  not blank  "
  not blank
  not blank
  not blank



SELECT 5

?column?	word_case	word_coalesce	word_function
""	default	default	default
" "	default	default	default
"value"	value	value	value
null	default	default	default
" not blank "	not blank	not blank	not blank