Example of building a simple UDF compared to the standard SQL function

proper_case_function.sql

 
CREATE TEMP FUNCTION
  PROPER(str STRING) AS ((
    SELECT
      STRING_AGG(CONCAT(UPPER(SUBSTR(w,1,1)), LOWER(SUBSTR(w,2))), ' '
      ORDER BY
        pos)
    FROM
      UNNEST(SPLIT(str, ' ')) w
    WITH
    OFFSET
      pos ));
SELECT
  string,
  PROPER(string) AS proper_string_udf,
  INITCAP(string) AS proper_string_function,
FROM (
  SELECT
    'i love data warehouses' AS string )