如何加入具有所有计数的另一个表的计数查询？

Question

我选择了少数表的计数，我有一个名为table_counts的表，它有两列名为table_name和table_count的列。我想要将查询的结果与table_counts表的table_name列结合起来。请看下面的例子。

select 'Table 1' as table_name, count(*) as table_count_from table_1 
union 
select 'Table 2' as table_name, count(*) as table_count_from table_2 
union 
select 'Table 3' as table_name, count(*) as table_count_from table_3 

------------------ 
++table_counts++++ 
------------------ 
table_name table count 
Table 1  10 
Table 2  20 
Table 3  30 

我必须使用table_name加入两件事情。如果我缺少一些东西，有人能帮助我吗？

Answer 1

你正在寻找类似的东西？

SELECT * 
    FROM table_counts cnt 
    LEFT OUTER JOIN (select 'Table 1' as table_name, count(*) as table_count_from table_1 
        union 
        select 'Table 2' as table_name, count(*) as table_count_from table_2 
        union 
        select 'Table 3' as table_name, count(*) as table_count_from table_3 
       ) subcnt 
    ON cnt.table_name = subcnt.table_name