SQL : 一屏显示多个表的计数

Question

我想在一个查询中显示多个表的计数。这是我的不同查询

SELECT count(*) FROM Table_1;
SELECT count(*) FROM Table_2;
SELECT count(*) FROM Table_3;

结果

Table_Name      Count
Table_1          51
Table_2          75
Table_3          108

如何实现？

Answer 1

一种简单的方法是 联合 您的查询：

SELECT 'Table_1' Table_Name, count(*) "Count" FROM Table_1
union all
SELECT 'Table_2', count(*) FROM Table_2
union all
SELECT 'Table_3', count(*) FROM Table_3;

Answer 2

一个 select 对具有不同列的 dual 的语句具有每个 table 的 select count(*) 的结果。

SELECT (SELECT Count(*)
        FROM   table_1) AS count1,
       (SELECT Count(*)
        FROM   table_2) AS count2,
       (SELECT Count(*)
        FROM   table_3) AS count3
FROM   dual;