Postgres 14

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select version();


version


PostgreSQL 14.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-4), 64-bit


CREATE TABLE test
(
  id INT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
  t_field TEXT
);
INSERT INTO test (t_field)
VALUES ('bar$foo$john$doe$xxx');  -- OP's own data
1 rows affected

INSERT INTO test (t_field)
SELECT 
  LEFT(MD5(RANDOM()::TEXT), FLOOR(RANDOM() * (5 - 3 + 1) + 3)::INT) || '$' ||
  LEFT(MD5(RANDOM()::TEXT), FLOOR(RANDOM() * (5 - 3 + 1) + 3)::INT) || '$' ||
  LEFT(MD5(RANDOM()::TEXT), FLOOR(RANDOM() * (5 - 3 + 1) + 3)::INT) || '$' ||
  LEFT(MD5(RANDOM()::TEXT), FLOOR(RANDOM() * (5 - 3 + 1) + 3)::INT) || '$' ||
  LEFT(MD5(RANDOM()::TEXT), FLOOR(RANDOM() * (5 - 3 + 1) + 3)::INT)
FROM 
  GENERATE_SERIES(1, 299999);  --<<== Vary here
   
  --
  -- Vary the GENERATE_SERIES(1, 299999) number if the fiddle run fails!
  --
  -- 299999 (+ 1 - OP) = 300,000 = large enough number to get reliable, consistent results
  -- and small enough so that the fiddle run doesn't fail too often.
  -- 
299999 rows affected

ANALYZE test;
--
--
--
-- Approach 1: The fastest - using OVERLAY(), STRPOS() & LENGTH()
--

SELECT
  t_field, 
  OVERLAY(t_field PLACING '-' 
    FROM 
      LENGTH(t_field) + 1 - STRPOS(REVERSE(t_field), '$')
         ) AS result
FROM test
LIMIT 2;


t_field
result


bar$foo$john$doe$xxx
bar$foo$john$doe-xxx

783e$2b4$04aa9$eaf$b64ff
783e$2b4$04aa9$eaf-b64ff


EXPLAIN (ANALYZE, TIMING OFF)
SELECT
  OVERLAY(t_field PLACING '-' 
    FROM 
      LENGTH(t_field) + 1 - STRPOS(REVERSE(t_field), '$')
         ) AS result
FROM test;


QUERY PLAN


Seq Scan on test  (cost=0.00..9718.00 rows=300000 width=32) (actual rows=300000 loops=1)

Planning Time: 0.041 ms

Execution Time: 745.485 ms

t_field	result
bar$foo$john$doe$xxx	bar$foo$john$doe-xxx
783e$2b4$04aa9$eaf$b64ff	783e$2b4$04aa9$eaf-b64ff