SQL Server 2019

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CREATE TABLE [UOMC](
    [From] [nchar](10) NULL,
    [To] [nchar](10) NULL,
    [Conv] [int] NULL,
    [PrimaryUOM]  [nchar](10) NULL,
    [ConvToPrimary] [int] NULL


)
;

INSERT INTO [UOMC]
           ([From],[To],[Conv],[PrimaryUOM],[ConvToPrimary])
     VALUES
           ('Feet','Inches',12,'Inches',12),
           ('Yards','Feet',3,'Inches',36),
           ('Miles','Yards',1760,'Inches',63360)
;
3 rows affected

  SELECT
    x.[From]                                  AS [From],
    y.[From]                                  AS [To],
    x.ConvToPrimary * 1.0 / y.ConvToPrimary   AS Conv,
    x.ConvToPrimary                           AS ConvToPrimary
  FROM
    UOMC   x
  INNER JOIN
    UOMC   y
      ON  x.PrimaryUOM = y.PrimaryUOM
;


From
To
Conv
ConvToPrimary


Feet
Feet
1.000000000000
12

Yards
Feet
3.000000000000
36

Miles
Feet
5280.000000000000
63360

Feet
Yards
0.333333333333
12

Yards
Yards
1.000000000000
36

Miles
Yards
1760.000000000000
63360

Feet
Miles
0.000189393939
12

Yards
Miles
0.000568181818
36

Miles
Miles
1.000000000000
63360


  SELECT
    x.[From]                                  AS [From],
    y.[From]                                  AS [To],
    x.ConvToPrimary * 1.0 / y.ConvToPrimary   AS Conv,
    x.PrimaryUOM                              AS PrimaryUOM,
    x.ConvToPrimary                           AS ConvToPrimary
  FROM
    UOMC   x
  INNER JOIN
    UOMC   y
      ON  x.PrimaryUOM = y.PrimaryUOM
  
  UNION
  
  SELECT * FROM UOMC
  
  ORDER BY
    ConvToPrimary, Conv
;


From
To
Conv
PrimaryUOM
ConvToPrimary


Feet
Miles
0.000189393939
Inches
12

Feet
Yards
0.333333333333
Inches
12

Feet
Feet
1.000000000000
Inches
12

Feet
Inches
12.000000000000
Inches
12

Yards
Miles
0.000568181818
Inches
36

Yards
Yards
1.000000000000
Inches
36

Yards
Feet
3.000000000000
Inches
36

Miles
Miles
1.000000000000
Inches
63360

Miles
Yards
1760.000000000000
Inches
63360

Miles
Feet
5280.000000000000
Inches
63360


WITH
  UOMC_expanded AS
(
  SELECT * FROM UOMC
  UNION ALL
  SELECT PrimaryUOM, PrimaryUOM, 1, PrimaryUOM, 1 FROM UOMC GROUP BY PrimaryUOM
)
  SELECT
    x.[From]                                  AS [From],
    y.[From]                                  AS [To],
    x.ConvToPrimary * 1.0 / y.ConvToPrimary   AS Conv,
    x.PrimaryUOM                              AS PrimaryUOM,
    x.ConvToPrimary                           AS ConvToPrimary
  FROM
    UOMC_expanded   x
  INNER JOIN
    UOMC_expanded   y
      ON  x.PrimaryUOM = y.PrimaryUOM
  ORDER BY
    ConvToPrimary, Conv
;


From
To
Conv
PrimaryUOM
ConvToPrimary


Inches
Miles
0.000015782828
Inches
1

Inches
Yards
0.027777777777
Inches
1

Inches
Feet
0.083333333333
Inches
1

Inches
Inches
1.000000000000
Inches
1

Feet
Miles
0.000189393939
Inches
12

Feet
Yards
0.333333333333
Inches
12

Feet
Feet
1.000000000000
Inches
12

Feet
Inches
12.000000000000
Inches
12

Yards
Miles
0.000568181818
Inches
36

Yards
Yards
1.000000000000
Inches
36

Yards
Feet
3.000000000000
Inches
36

Yards
Inches
36.000000000000
Inches
36

Miles
Miles
1.000000000000
Inches
63360

Miles
Yards
1760.000000000000
Inches
63360

Miles
Feet
5280.000000000000
Inches
63360

Miles
Inches
63360.000000000000
Inches
63360

From	To	Conv	ConvToPrimary
Feet	Feet	1.000000000000	12
Yards	Feet	3.000000000000	36
Miles	Feet	5280.000000000000	63360
Feet	Yards	0.333333333333	12
Yards	Yards	1.000000000000	36
Miles	Yards	1760.000000000000	63360
Feet	Miles	0.000189393939	12
Yards	Miles	0.000568181818	36
Miles	Miles	1.000000000000	63360

From	To	Conv	PrimaryUOM	ConvToPrimary
Inches	Miles	0.000015782828	Inches	1
Inches	Yards	0.027777777777	Inches	1
Inches	Feet	0.083333333333	Inches	1
Inches	Inches	1.000000000000	Inches	1
Feet	Miles	0.000189393939	Inches	12
Feet	Yards	0.333333333333	Inches	12
Feet	Feet	1.000000000000	Inches	12
Feet	Inches	12.000000000000	Inches	12
Yards	Miles	0.000568181818	Inches	36
Yards	Yards	1.000000000000	Inches	36
Yards	Feet	3.000000000000	Inches	36
Yards	Inches	36.000000000000	Inches	36
Miles	Miles	1.000000000000	Inches	63360
Miles	Yards	1760.000000000000	Inches	63360
Miles	Feet	5280.000000000000	Inches	63360
Miles	Inches	63360.000000000000	Inches	63360