CREATE TABLE Grid
(v1 SMALLINT NOT NULL CHECK (v1 > 0), 
v2 SMALLINT NOT NULL CHECK (v2 > 0), 
 v_cover SMALLINT DEFAULT 0 NOT NULL,
PRIMARY KEY (v1, v2), 
CHECK (v1 < v2));

INSERT INTO Grid (v1, v2)
VALUES (1, 2), (1, 4), (2, 3), (2, 5), (2, 6); 

CREATE VIEW Vertexes (v)
AS
SELECT v1,  v_cover
  FROM Grid
UNION
SELECT v2,  v_cover
  FROM Grid; 

CREATE VIEW Vertex_Degrees (v, degree)
AS
SELECT V.v, COUNT(*) AS degree
  FROM Grid AS G, Vertexes AS V
 WHERE V.v IN (G.v1, G.v2)
 GROUP BY V.v;

CREATE TABLE #Grid
(v1 CHAR(1) NOT NULL, -- CHECK (v1 > 0), 
v2 CHAR(1) NOT NULL, --  CHECK (v2 > 0), 
PRIMARY KEY (v1, v2)--, 
--CHECK (v1 < v2)
);

INSERT INTO #Grid
SELECT 'A', 'B'
UNION ALL SELECT 'A', 'C'
UNION ALL SELECT 'A', 'D'
UNION ALL SELECT 'B', 'E'
UNION ALL SELECT 'B', 'F'
UNION ALL SELECT 'C', 'G'
UNION ALL SELECT 'C', 'H'
UNION ALL SELECT 'D', 'I'
UNION ALL SELECT 'D', 'J'
UNION ALL SELECT 'E', 'K'
UNION ALL SELECT 'F', 'L'
UNION ALL SELECT 'G', 'K'
UNION ALL SELECT 'G', 'M'
UNION ALL SELECT 'H', 'L'
UNION ALL SELECT 'I', 'M'
UNION ALL SELECT 'J', 'M'
UNION ALL SELECT 'K', 'N'
UNION ALL SELECT 'K', 'O'
UNION ALL SELECT 'L', 'O'
UNION ALL SELECT 'M', 'O' 
UNION ALL SELECT 'O', 'Q'
UNION ALL SELECT 'Q', 'R'
UNION ALL SELECT 'J', 'P'
UNION ALL SELECT 'N', 'Q'
UNION ALL SELECT 'N', 'R'
UNION ALL SELECT 'P', 'S'
UNION ALL SELECT 'P', 'T'
UNION ALL SELECT 'Q', 'W'
UNION ALL SELECT 'Q', 'U'
UNION ALL SELECT 'R', 'U'
UNION ALL SELECT 'R', 'V'
UNION ALL SELECT 'S', 'V'
UNION ALL SELECT 'S', 'R'
UNION ALL SELECT 'T', 'V'
UNION ALL SELECT 'T', 'Y'
UNION ALL SELECT 'U', 'W'
UNION ALL SELECT 'U', 'X'
UNION ALL SELECT 'V', 'X'
UNION ALL SELECT 'V', 'Y'
UNION ALL SELECT 'X', 'W'
UNION ALL SELECT 'W', 'Z'
UNION ALL SELECT 'Y', 'Z'

V   V,R,S,T,X,Y
Q   Q,N,O,R,U,W
M   M,G,I,J,O
K   K,E,G,N,O
P   P,J,S,T
L   L,F,H,O
D   D,A,I,J
C   C,A,G,H
B   B,A,E,F
Z   Z,W,Y