从多个表中选择count(*)

SELECT  (
SELECT COUNT(*)
FROM   tab1
) AS count1,
(
SELECT COUNT(*)
FROM   tab2
) AS count2
FROM    dual

select (select count(*) from tab1) count_1, (select count(*) from tab2) count_2 from dual;

我很快想到了:

Select (select count(*) from Table1) as Count1, (select count(*) from Table2) as Count2

注意:我在SQL Server中测试了这个，所以From Dual是不必要的(因此存在差异)。

作为附加信息，要在SQL Server中完成同样的事情，您只需要删除查询的“FROM dual”部分。

我的经验是使用SQL Server，但是你能做到:

select (select count(*) from table1) as count1,
(select count(*) from table2) as count2

在SQL Server我得到的结果，你是后。

如果表(或者至少是一个键列)是相同类型的，那么就先做联合，然后计数。

select count(*)
from (select tab1key as key from schema.tab1
union all
select tab2key as key from schema.tab2
)

或者把你的语句加上另一个和()。

select sum(amount) from
(
select count(*) amount from schema.tab1 union all select count(*) amount from schema.tab2
)

只是因为它略有不同:

SELECT 'table_1' AS table_name, COUNT(*) FROM table_1
UNION
SELECT 'table_2' AS table_name, COUNT(*) FROM table_2
UNION
SELECT 'table_3' AS table_name, COUNT(*) FROM table_3

它给出了转置的答案(每个表一行而不是一列)，否则我不认为它有多大不同。我认为在性能方面，它们应该是相等的。

其他略有不同的方法:

with t1_count as (select count(*) c1 from t1),
t2_count as (select count(*) c2 from t2)
select c1,
c2
from   t1_count,
t2_count
/


select c1,
c2
from   (select count(*) c1 from t1) t1_count,
(select count(*) c2 from t2) t2_count
/

因为我找不到其他答案了。

如果你不喜欢子查询而且在每个表中有主键，你可以这样做:

select count(distinct tab1.id) as count_t1,
count(distinct tab2.id) as count_t2
from tab1, tab2

但是就性能而言，我认为Quassnoi的解决方案更好，也是我会使用的解决方案。

SELECT (SELECT COUNT(*) FROM table1) + (SELECT COUNT(*) FROM table2) FROM dual;

这是我的分享

选项1 -计数从相同的域从不同的表

select distinct(select count(*) from domain1.table1) "count1", (select count(*) from domain1.table2) "count2"
from domain1.table1, domain1.table2;

选项2 -同一表从不同的域计数

select distinct(select count(*) from domain1.table1) "count1", (select count(*) from domain2.table1) "count2"
from domain1.table1, domain2.table1;

选项3 -计数从不同的领域为同一表与“联合所有”有行计数

select 'domain 1'"domain", count(*)
from domain1.table1
union all
select 'domain 2', count(*)
from domain2.table1;

享受SQL，我总是这样做:)

为了完整起见，这个查询将创建一个查询，为您提供给定所有者的所有表的计数。

select
DECODE(rownum, 1, '', ' UNION ALL ') ||
'SELECT ''' || table_name || ''' AS TABLE_NAME, COUNT(*) ' ||
' FROM ' || table_name  as query_string
from all_tables
where owner = :owner;

输出是这样的

SELECT 'TAB1' AS TABLE_NAME, COUNT(*) FROM TAB1
UNION ALL SELECT 'TAB2' AS TABLE_NAME, COUNT(*) FROM TAB2
UNION ALL SELECT 'TAB3' AS TABLE_NAME, COUNT(*) FROM TAB3
UNION ALL SELECT 'TAB4' AS TABLE_NAME, COUNT(*) FROM TAB4

然后你可以运行它来得到你的计数。有时它只是一个方便的脚本。

select @count = sum(data) from
(
select count(*)  as data from #tempregion
union
select count(*)  as data from #tempmetro
union
select count(*)  as data from #tempcity
union
select count(*)  as data from #tempzips
) a

与不同的表进行JOIN

SELECT COUNT(*) FROM (
SELECT DISTINCT table_a.ID  FROM table_a JOIN table_c ON table_a.ID  = table_c.ID   );

Declare @all int
SET @all = (select COUNT(*) from tab1) + (select count(*) from tab2)
Print @all

或

SELECT (select COUNT(*) from tab1) + (select count(*) from tab2)

--============= FIRST WAY (Shows as Multiple Row) ===============
SELECT 'tblProducts' [TableName], COUNT(P.Id) [RowCount] FROM tblProducts P
UNION ALL
SELECT 'tblProductSales' [TableName], COUNT(S.Id) [RowCount] FROM tblProductSales S




--============== SECOND WAY (Shows in a Single Row) =============
SELECT
(SELECT COUNT(Id) FROM   tblProducts) AS ProductCount,
(SELECT COUNT(Id) FROM   tblProductSales) AS SalesCount

    select
t1.Count_1,t2.Count_2
from
(SELECT count(1) as Count_1 FROM tab1) as t1,
(SELECT count(1) as Count_2 FROM tab2) as t2

SELECT  (
SELECT COUNT(*)
FROM   tbl1
)
+
(
SELECT COUNT(*)
FROM   tbl2
)
as TotalCount