Rename columns from camelCase to underscore - PostgreSQL

rename_columns.sql

WITH from_table AS (

  SELECT 'janky_table'::text AS name

)
SELECT 'ALTER TABLE "' || f.name || '" RENAME COLUMN "' || cols.column_name || '" TO "' || cols.regular_pgstyle || '";' AS stmt 
  FROM (SELECT column_name, 
               lower(regexp_replace(column_name, E'([A-Z])', E'\_\\1','g')) As regular_pgstyle
          FROM information_schema.columns,
               from_table f
         WHERE table_name = f.name) cols,
        from_table f
 WHERE cols.column_name != cols.regular_pgstyle;

regular_pgstyle borrowed from here:

http://www.postgresonline.com/journal/archives/170-Of-Camels-and-People-Converting-back-and-forth-from-Camel-Case,-Pascal-Case-to-underscore-lower-case.html

Sample output:

ALTER TABLE "janky_table" RENAME COLUMN "userId" TO "user_id";

I extended it for my use case:

No lowercase in the beginning of column: ( TheHouse -> the_house instead of _the_house)

lower(regexp_replace(column_name, E'([a-z])([A-Z])', E'\\1\_\\2','g')) As regular_pgstyle

Better handling of digits at the beginning( 2022TheHouse -> _2022_the_house instead of 2022the_house)

           regexp_replace(
                   lower(regexp_replace(column_name, E'([a-z])([A-Z])', E'\\1\_\\2','g')),
                   E'^([0-9]+)', E'\_\\1\_','g'
                )

Then I put it in anonymous execution block:

DO $$DECLARE r record;
BEGIN
    FOR r IN
WITH from_table AS (

  SELECT 'janky_table'::text AS name

)
SELECT 'ALTER TABLE ' || f.name || ' RENAME COLUMN "' || cols.column_name || '" TO ' || cols.regular_pgstyle  AS stmt
  FROM (SELECT column_name,
               regexp_replace(
                   lower(regexp_replace(column_name, E'([a-z])([A-Z])', E'\\1\_\\2','g')),
                   E'^([0-9]+)', E'\_\\1\_','g'
                )
                   As regular_pgstyle
          FROM information_schema.columns,
               from_table f
         WHERE table_name = f.name) cols,
        from_table f
 WHERE cols.column_name != cols.regular_pgstyle
    LOOP
        EXECUTE r.stmt;
    END LOOP;
END$$;