在单个查询中获取两个SQL表中的列数？

Question

我已经写了两个SQL语句：

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

两个语句返回我想要的数据，但我想知道如何与两个单元返回单个表：table1Count和table2Count从一个单一的查询。

我该如何构建查询？

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：

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

Answer 2

随着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; 

会产生：

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