Oracle PL / SQL：两个表之间的count（*）

Question

尝试计算2个表之间的计数差异。

关注this，但获得00923. 00000 - "FROM keyword not found where expected"

SELECT ( SELECT count(*) FROM XE_ERR_OVLP WHERE FLAG = 'E') 
- (SELECT count(*) FROM XE_ERR_RANG WHERE FLAG = 'H' ) as cnt;

如何实现这一目标？

Answer 1

那是：

SELECT ( SELECT count(*) FROM XE_ERR_OVLP WHERE FLAG = 'E') 
  - (SELECT count(*) FROM XE_ERR_RANG WHERE FLAG = 'H' ) as cnt 
  from dual;

与其他数据库相比，Oracle需要from子句。您可以使用虚拟表dual。

Answer 2

您需要添加FROM DUAL 您的查询应如下所示

SELECT ( SELECT count(*) FROM XE_ERR_OVLP WHERE FLAG = 'E') 
- (SELECT count(*) FROM XE_ERR_RANG WHERE FLAG = 'H' ) as cnt
FROM DUAL;

Answer 3

您可以使用UNION ALL和SUM：

SELECT SUM(c) AS cnt
FROM (SELECT 1 AS c FROM XE_ERR_OVLP WHERE FLAG = 'E'
     UNION ALL
     SELECT -1 FROM XE_ERR_RANG WHERE FLAG = 'H') sub;

Answer 4

我们还可以仅使用 SUM （）来计算计数差异，如下所示。

select ( ( select sum(1) XE_ERR_OVLP WHERE FLAG = 'E' ) 
       - ( select sum(1) XE_ERR_RANG WHERE FLAG = 'H' ) 
    ) cnt from dual;