Question

我有一个Oracle数据库，我需要运行带有子选择的select，但是，它们都不共享同一个表Universe，因此，我需要做这样的事情：

SELECT  (
SELECT COUNT(*)
FROM   user_table
) AS tot_user,
(
SELECT COUNT(*)
FROM   cat_table
) AS tot_cat,
(
SELECT COUNT(*)
FROM   course_table
) AS tot_course

我知道这在其他数据库中是可行的，但对于Oracle我需要这样的东西。

有人可以帮忙吗？

Answer 1

要在oracle中使用此功能，请将from dual添加到结尾：

SELECT  (SELECT COUNT(*)
         FROM   user_table
        ) AS tot_user,
        (SELECT COUNT(*)
         FROM   cat_table
        ) AS tot_cat,
        (SELECT COUNT(*)
         FROM   course_table
        ) AS tot_course
FROM dual;

与数据库无关的编写查询的方法是：

select tot_user, tot_cat, tot_course
from (SELECT COUNT(*) as tot_user
      FROM   user_table
     ) u cross join
     (SELECT COUNT(*) as tot_cat
      FROM   cat_table
     ) c cross join
     (SELECT COUNT(*) as tot_course
      FROM   course_table
     ) ct;

具有不同Universe的子查询

1 个答案: