DB2 SQL SELECT COUNT多個表

Question

的工會，我需要返回的記錄數一定條件下多個表

select count(*) c from table1 
where exists (select * from crosstable where crosstable.refid = table1.id) 
and crosstable.year = 2014 
union 
select count(*) c from table2 
where exists (select * from crosstable where crosstable.refid = table2.id) 
and crosstable.year = 2014 
union 
select count(*) c from table3 
where exists (select * from crosstable where crosstable.refid = table3.id) 
and crosstable.year = 2014 

這回我唯一的整數值的一個結果從表中。所以如果table1返回'1'，table2和table3返回'5'，我會得到'1'，'5'而不是'1'，'5'，'5'。

而且它好好嘗試似乎工作進行

select sum(c) from (previous query)) 

我試圖用一個sysdummy表，但我不明白的語法安靜正確的，我找不到這個問題的任何很好的例子。可能是我管這完全錯了..

最後我需要的結果是1支單數，這是每個子查詢的聯合零件計數

Answer 1

您的查詢

select sum(c) from (previous query) 

很好 - 差不多。 DB2預計子查詢中有一個別名，所以嘗試：

select sum(c) from (previous query) x 

順便說一句，你union幾乎肯定需要是union all。 union消除重複。

Answer 2

請嘗試以下

with temp as (
    select count(*) c from table1 
    where exists (select * from crosstable where crosstable.refid = table1.id) 
    and crosstable.year = 2014 
    union all 
    select count(*) c from table2 
    where exists (select * from crosstable where crosstable.refid = table2.id) 
    and crosstable.year = 2014 
    union all 
    select count(*) c from table3 
    where exists (select * from crosstable where crosstable.refid = table3.id) 
    and crosstable.year = 2014 
) 
select sum(c) as final_count from temp;