SQL中多列的逐对交点数

Question

说我有一个带有多个表的SQL数据库，并且每个表都有一个列code。我要生成的表格是显示每对code列之间共享的代码数。即成对相交计数图：

       table1 table2 table3 table4
table1     10      2      3      5
table2      2     10      4      1
table3      3      4     10      2
table4      5      1      2     10

我可以使用例如单独获取每个值

WITH abc AS 
(
SELECT code FROM table1
INTERSECT
SELECT code FROM table2
)

SELECT COUNT(*) AS table1Xtable2 FROM abc

但是有没有一个查询将生成所需的完整输出作为表？

Answer 1

以下内容获取表之间的all组合：

select t1, t2, t3, t4, count(*) 
from (select code, max(t1) as t1, max(t2) as t2, max(t3) as t3, max(t4) as t4
      from ((select code, 1 as t1, 0 as t2, 0 as t3, 0 as t4
             from table1
            ) union all
            (select code, 0 as t1, 1 as t2, 0 as t3, 0 as t4
             from table2
            ) union all
            (select code, 0 as t1, 0 as t2, 1 as t3, 0 as t4
             from table3
            ) union all
            (select code, 0 as t1, 0 as t2, 0 as t3, 1 as t4
             from table4
            )
           ) t
      group by code
     ) t
group by t1, t2, t3, t4;

对于您的特定问题，可以使用：

with t as (
      select code, 'table1' as tablename from table1 union all
      select code, 'table2' as tablename from table2 union all
      select code, 'table3' as tablename from table3 union all
      select code, 'table4' as tablename from table4 
     )
select t1.tablename,
       sum(case when t2.tablename = 'table1' then 1 else 0 end) as t1,
       sum(case when t2.tablename = 'table2' then 1 else 0 end) as t2,
       sum(case when t2.tablename = 'table3' then 1 else 0 end) as t3,
       sum(case when t2.tablename = 'table4' then 1 else 0 end) as t4
from t t1 join
     t t2
on t1.code = t2.code
group by t1.tablename

注意，以上假设code在表中是唯一的。如果重复，则可以将union all替换为union。