DMLFill

USE tempdb;
GO
IF OBJECT_ID('DMLfill', 'P') IS NOT NULL
  DROP PROC DMLfill
GO
CREATE PROC DMLfill
  @StudentCount INT = 100,
  @GroupCount INT = 10,
  @ScoreCount INT = 100
AS

DELETE FROM Student;
DELETE FROM GroupStudent;

;WITH CTE AS(
  SELECT 1 N
  UNION ALL
  SELECT N+1 FROM CTE WHERE N<@GroupCount
)

INSERT GroupStudent(Number)
SELECT CONCAT('GROUP #', N)
FROM CTE
OPTION(MAXRECURSION 30000)

;WITH CTE AS(
  SELECT 1 N
  UNION ALL
  SELECT N+1 FROM CTE WHERE N<@StudentCount
)

INSERT Student(GroupId, FIO)
SELECT GS.id, CONCAT('ФИО|', GS.id, '|', N)
FROM CTE
  JOIN (
    SELECT ROW_NUMBER()OVER(ORDER BY id)GN, *
    FROM GroupStudent
  ) GS ON GS.GN = (N-1)%@GroupCount + 1

OPTION(MAXRECURSION 30000)