获取单个查询中两个SQL表中的列数？

Question

我写了两个SQL语句：

SELECT Count(*) AS table1Count FROM table1 WHERE foo=1;
SELECT Count(*) AS table2Count FROM table2 WHERE bar=2;

两个语句都返回我想要的数据，但我想知道如何返回一个包含两个单元格的表：table1Count和table2Count来自单个查询。

如何构建查询？

Answer 1

SELECT (SELECT Count(*) AS table1Count FROM table1 WHERE foo=1) AS table1Count, 
       (SELECT Count(*) AS  table2Count FROM table2 WHERE bar=2) AS table2Count;

给出类似的东西：

 table1count | table2count 
-------------+-------------
           4 |           6
(1 row)

Answer 2

使用UNION ALL：

SELECT 'Table1' AS "Table", Count(*) As "Count" FROM table1 WHERE foo=1
UNION ALL
SELECT 'Table2' AS "Table", Count(*) As "Count" FROM table2 WHERE bar=2;

将产生：

Table  | Count
---------------
Table1 | 1
Table2 | 2