如何獲得聯合操作後的記錄數量？

Question

我有這樣的查詢：

select author1 
from books_group 
where category='cse' 
union 
select author2 
from books_group 
where category='cse' 
union 
select author3 
from books_group 
where category='cse' 

上面的查詢聯盟的所有那些來自三個選擇命令記錄..

我的任務就是來算，我們以後有記錄的數量從上面的SQL命令的執行...

，我想下面的查詢，但它給出了一個錯誤..

「SELECT COUNT（*）（從books_group選擇作者1類別爲」CSE工會選擇author2從books_group where category ='cse'union select_3 author_3 from books_group where category ='cse'）「

然後，如何獲得聯合操作後錄音機的數量。

Answer 1

你被關閉，你需要指定一個別名，那麼再選擇：

select 
    count(*) 
from 
    (
    select author1 from books_group where category='cse' union 
    select author2 from books_group where category='cse' union 
    select author3 from books_group where category='cse' 
    ) a 

Answer 2

試試這個：

select count(*) from 
(select author1 from books_group where category='cse' 
union 
select author2 from books_group where category='cse' 
union 
select author3 from books_group where category='cse')A