SQL:从单个列中获取所有对和三元组，并计算它们在另一列中的出现频率

SELECT A, B FROM 表名;

SELECT t1.A, t1.B, t2.B
FROM 表名 t1, 表名 t2
WHERE t1.A = t2.A AND t1.B <> t2.B;

SELECT t1.A, t1.B, t2.B, t3.B
FROM 表名 t1, 表名 t2, 表名 t3
WHERE t1.A = t2.A AND t2.A = t3.A AND t1.B <> t2.B AND t2.B <> t3.B AND t1.B <> t3.B;

SELECT t.A, t.B, COUNT(t.C) AS frequency
FROM (
    SELECT t1.A, t1.B, t2.B, t3.B, t1.C
    FROM 表名 t1, 表名 t2, 表名 t3
    WHERE t1.A = t2.A AND t2.A = t3.A AND t1.B <> t2.B AND t2.B <> t3.B AND t1.B <> t3.B
) t
GROUP BY t.A, t.B;