WITH cte AS
(
SELECT 'A' AS team
UNION ALL SELECT 'B'
UNION ALL SELECT 'C'
UNION ALL SELECT 'D'
)
SELECT * FROM cte a,cte b
WHERE a.team<b.team 
/*
team    team
A    B
A    C
A    D
B    C
B    D
C    D
*/

------解决方案--------------------
SQL code
IF object_id('tc') IS NOT NULL 
  DROP TABLE tc 

GO

CREATE TABLE tc (
  team VARCHAR(10))

INSERT INTO tc
SELECT 'A'
UNION ALL
SELECT 'B'
UNION ALL
SELECT 'C'
UNION ALL
SELECT 'D'

SELECT Count(1)
FROM   tc a
       INNER JOIN tc b
         ON a.team < b.team