SQL Server 2019

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CREATE TABLE test (
  col VARCHAR(100)
);

INSERT INTO test VALUES
  ('8'), ('476'), ('4767'), ('45907392'), ('845907392');
5 rows affected

SELECT REVERSE(SUBSTRING(REVERSE(col), 7, 3)) 
  + CASE WHEN LEN(col)>6 THEN '-' ELSE '' END 
  + REVERSE(SUBSTRING(REVERSE(col), 4, 3)) 
  + CASE WHEN LEN(col)>3 THEN '-' ELSE '' END 
  + REVERSE(SUBSTRING(REVERSE(col), 1, 3))
FROM test

(No column name)

8

476

4-767

45-907-392

845-907-392

CREATE FUNCTION dbo.GetFormatTripleDash (@str varchar(255))
RETURNS VARCHAR(255)
AS
BEGIN
  DECLARE @retStr VARCHAR(255) = REVERSE(SUBSTRING(REVERSE(@str), 7, 3)) 
    + CASE WHEN LEN(@str)>6 THEN '-' ELSE '' END 
    + REVERSE(SUBSTRING(REVERSE(@str), 4, 3)) 
    + CASE WHEN LEN(@str)>3 THEN '-' ELSE '' END 
    + REVERSE(SUBSTRING(REVERSE(@str), 1, 3))
  RETURN(@retStr)
END
SELECT dbo.GetFormatTripleDash(col)
FROM test

(No column name)

8

476

4-767

45-907-392

845-907-392

CREATE FUNCTION dbo.GetFormatDash (@str varchar(255), @partSize INT = 3)
RETURNS VARCHAR(255)
AS
BEGIN
  DECLARE @startSize INT = 0;
  DECLARE @retStr VARCHAR(255) = '';

  WHILE @startSize < LEN(@str)
  BEGIN
    SET @retStr = REVERSE(SUBSTRING(REVERSE(@str), @startSize + 1, @partSize)) + CASE WHEN @startSize > 0 THEN '-' ELSE '' END + @retStr;
    SET @startSize = @startSize + @partSize;
  END

  RETURN(@retStr)
END 
SELECT dbo.GetFormatDash(col, 3) 
FROM test

(No column name)

8

476

4-767

45-907-392

845-907-392

SELECT dbo.GetFormatDash('12345678901234567890', DEFAULT)
SELECT dbo.GetFormatDash('12345678901234567890', 3)
SELECT dbo.GetFormatDash('12345678901234567890', 5)

(No column name)

12-345-678-901-234-567-890

(No column name)

12-345-678-901-234-567-890

(No column name)

12345-67890-12345-67890