(SQL) フィールド内で文字列形式が複数出現する位置を特定する

これは再帰 CTE で解決できます

DECLARE @tbl TABLE (Case_Reference NVARCHAR(MAX),Narrative NVARCHAR(MAX));
INSERT INTO @tbl VALUES
 (N'C1',N'01/02/2000  Some text with     blanks 02/03/2000  More text 03/04/2000  An even more')
,(N'C2',N'01/02/2000  Test for C2 02/03/2000  One more for C2 03/04/2000  An even more 04/05/2000  Blah')
,(N'C3',N'01/02/2000  Test for C3 02/03/2000  One more for C3 03/04/2000  An even more')
 ;

WITH recCTE AS
(
    SELECT 1 AS Step,Case_Reference,Narrative,CAST(1 AS BIGINT) AS StartsAt,NewPos.EndsAt+10 AS EndsAt,LEN(Narrative) AS MaxLen
          ,SUBSTRING(Narrative,NewPos.EndsAt+10+1,999999) AS RestString
    FROM @tbl AS tbl
    CROSS APPLY(SELECT PATINDEX('%[0-3][0-9]/[0-1][0-9]/[1-2][0-9][0-9][0-9]  %',SUBSTRING(Narrative,12,9999999))) AS NewPos(EndsAt)

    UNION ALL

    SELECT r.Step+1,r.Case_Reference,r.Narrative,r.EndsAt+1,CASE WHEN NewPos.EndsAt>0 THEN r.EndsAt+NewPos.EndsAt+10 ELSE r.MaxLen END,r.MaxLen
          ,SUBSTRING(r.RestString,NewPos.EndsAt+10+1,999999) 
    FROM recCTE AS r
    CROSS APPLY(SELECT PATINDEX('%[0-3][0-9]/[0-1][0-9]/[1-2][0-9][0-9][0-9]  %',SUBSTRING(r.RestString,12,99999999))) AS NewPos(EndsAt)
    WHERE r.EndsAt<r.MaxLen
)
SELECT Step,Case_Reference,StartsAt,EndsAt
      ,SUBSTRING(Narrative,StartsAt,EndsAt-StartsAt+1) AS OutputString 
FROM recCTE

ORDER BY Case_Reference,Step

結果

+------+----------------+----------+--------+---------------------------------------+
| Step | Case_Reference | StartsAt | EndsAt | OutputString                          |
+------+----------------+----------+--------+---------------------------------------+
| 1    | C1             | 1        | 38     | 01/02/2000  Some text with     blanks |
+------+----------------+----------+--------+---------------------------------------+
| 2    | C1             | 39       | 60     | 02/03/2000  More text                 |
+------+----------------+----------+--------+---------------------------------------+
| 3    | C1             | 61       | 84     | 03/04/2000  An even more              |
+------+----------------+----------+--------+---------------------------------------+
| 1    | C2             | 1        | 24     | 01/02/2000  Test for C2               |
+------+----------------+----------+--------+---------------------------------------+
| 2    | C2             | 25       | 52     | 02/03/2000  One more for C2           |
+------+----------------+----------+--------+---------------------------------------+
| 3    | C2             | 53       | 77     | 03/04/2000  An even more              |
+------+----------------+----------+--------+---------------------------------------+
| 4    | C2             | 78       | 93     | 04/05/2000  Blah                      |
+------+----------------+----------+--------+---------------------------------------+
| 1    | C3             | 1        | 24     | 01/02/2000  Test for C3               |
+------+----------------+----------+--------+---------------------------------------+
| 2    | C3             | 25       | 52     | 02/03/2000  One more for C3           |
+------+----------------+----------+--------+---------------------------------------+
| 3    | C3             | 53       | 76     | 03/04/2000  An even more              |
+------+----------------+----------+--------+---------------------------------------+