如何将计数查询与另一个具有所有计数的表连接起来？

Question

我正在选择几个表的计数，并且我有一个名为 table_counts 的表，其中有两个名为 table_name 和 table_count 的列。我想将查询结果与 table_counts 表的 table_name 列连接起来。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 来连接这两个东西。如果我缺少一些东西，有人可以帮助我吗？

Answer 1

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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