如何计算行数

Question

我如何计算三个表中的行数并返回三个行计数的总和？

Answer 1

这将返回您的数据库上的每个表计数，只需添加WHERE来过滤您想要的那些

http://www.dba-oracle.com/t_count_rows_all_tables_in_schema.htm

select
   table_name,
   to_number(
   extractvalue(
      xmltype(
         dbms_xmlgen.getxml('select count(*) c from '||table_name))
    ,'/ROWSET/ROW/C')) row_count
from 
   user_tables
order by 
   table_name;

只需将其添加到CTE即可获得SUM

WITH cte AS ( 
    select
       table_name,
       to_number(
       extractvalue(
          xmltype(
             dbms_xmlgen.getxml('select count(*) c from '||table_name))
        ,'/ROWSET/ROW/C')) row_count
    from 
       user_tables
    WHERE table_name in ('table1', 'table2', 'table3' )
)
SELECT SUM(row_count)
FROM cte

Answer 2

space

Answer 3

由于表格的行数作为单行结果返回，您可以将三个结果交叉连接，并将它们与+运算符相加：

SELECT     a.cnt + b.cnt + c.cnt
FROM       (SELECT COUNT(*) AS cnt FROM table_a) a
CROSS JOIN (SELECT COUNT(*) AS cnt FROM table_b) b
CROSS JOIN (SELECT COUNT(*) AS cnt FROM table_c) c

Answer 4

select sum(v.cnt) as total_sum
from 
 (select count (*) as cnt from <<table1>>
  union all
  select count (*) as cnt from <<table2>>
  union all
  select count (*) as cnt from <<table3>>) v

Answer 5

select 
cnt1 + cnt2 + cnt3
as mycnt
from 
(SELECT COUNT (*) as cnt1 FROM s1.t1),
(SELECT COUNT (*) as cnt2 FROM s1.t2),
(SELECT COUNT (*) as cnt3 FROM s1.t3)

我最终使用的是什么。谢谢大家。