SQL Server 2014

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CREATE FUNCTION dbo.fnPattern_Split
(
  @str     VARCHAR(MAX),
  @pattern VARCHAR(100)
)
RETURNS @tbl TABLE (
 ordinal INT,
 value VARCHAR(MAX),
 match BIT
)
WITH SCHEMABINDING
AS
BEGIN
  DECLARE @value NVARCHAR(MAX)
        , @splitvalue NVARCHAR(MAX)
        , @startpos INT = 0
        , @endpos INT = 0
        , @ordinal INT = 0
        , @foundend BIT = 0
        , @patminlen INT = ISNULL(NULLIF(LEN(REPLACE(@pattern,'%','')),0),1);
  WHILE (LEN(@str) > 0)
  BEGIN
    
    SET @startpos = ISNULL(NULLIF(PATINDEX('%'+@pattern+'%', @str),0), LEN(@str)+1);
    
    IF @startpos < LEN(@str)
    BEGIN
        SET @foundend = 0;
        SET @endpos = @startpos+@patminlen-1;
        
        WHILE @endpos < LEN(@str) AND @foundend = 0
        BEGIN
          IF SUBSTRING(@str, @startpos, 1+@endpos-@startpos) LIKE @pattern
            SET @foundend = 1;
          ELSE
            SET @endpos += 1;
        END
    END
    ELSE SET @endpos = LEN(@str);
    
    IF @startpos > 1
    BEGIN
      SET @ordinal += 1;
      SET @value = LEFT(@str, @startpos-1);
      INSERT INTO @tbl (ordinal, value, match)
                VALUES (@ordinal, @value, 0);
    END
    
    IF @endpos >= @startpos
    BEGIN
      SET @ordinal += 1;
      SET @splitvalue = SUBSTRING(@str, @startpos, 1+@endpos-@startpos);
      INSERT INTO @tbl (ordinal, value, match)
                VALUES (@ordinal, @splitvalue, 1);
    END
    
    SET @str = SUBSTRING(@str, @endpos+1, LEN(@str));
  END;
  RETURN;
END;

result
'A or B' OR 'C or D' OR 'E or F'