How to solve the task of filling in gaps in a brute-force way without ready-made functions in SQL?

If you need to fill gaps in a sequence of values (such as dates or numbers) in SQL without using built-in functions (like row generators), you can apply a "brute-force" method using self-joins or loops.

Example: there is a table with dates, but some dates are missing. To fill the gaps, you can:

1. Create a helper table with a range of numbers (for example, from 0 to N).
2. Use this table and the minimum date from the original data to generate all dates in the range.
3. Perform a left join with the original table to get existing values and NULLs for missing dates.

Example in SQL (PostgreSQL-like syntax):

-- Helper table with numbers
WITH nums AS (
  SELECT 0 AS n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
),
min_max AS (
  SELECT MIN(date_col) AS min_date, MAX(date_col) AS max_date FROM data_table
),
dates AS (
  SELECT min_date + INTERVAL '1 day' * n AS date_val
  FROM nums, min_max
  WHERE min_date + INTERVAL '1 day' * n <= max_date
)
SELECT d.date_val, dt.value
FROM dates d
LEFT JOIN data_table dt ON dt.date_col = d.date_val
ORDER BY d.date_val;

If CTEs or row generation are not available, you can create a temporary table with the required range manually and use a similar approach.