如何在一个查询中计算来自两个表的行?

问题描述：

我知道，如果两个表中的列数相等，则可以在select语句上使用UNION.另外，另一个选择是在select子句中使用子查询.我还能使用什么?

I know that one can use UNION on a select statement if count of columns in two tables is equal. Also, another option is using sub-query in the select clause. What else can I use?

示例:

tabel1  table2
id  1       1 
    2       2
    3       3

我需要在一个查询中从两个表中获取总行数:

I need to get the number of total rows from both tables in one query:

...COUNT(table1.id) as tbc1, COUNT(table2.id) as tbc2...

答

使用子查询，如果需要，请添加FROM DUAL:

Use sub-queries and if it needs add FROM DUAL:

SELECT 
    (SELECT COUNT(*) FROM TABLE1) As Table1Count, 
    (SELECT COUNT(*) FROM TABLE2) As Table2Count
[FROM DUAL]

如何在一个查询中计算来自两个表的行?

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