SQL：選擇具有條件的行？

Question

想象我有如下表：

我搜索是：

select count(id) where "colX is never 20 AND colY is never 31" 

預期結果：

3 (= id numbers 5,7,8) 

而且

select count(id) where "colX contains (at least once) 20 AND colY contains (at least once) 31" 

預期結果：

1 (= id number 2) 

我感謝所有幫助

Answer 1

這是一個「爲例套，內集「子查詢。最好的方法是使用having子句進行聚合，因爲它是最通用的方法。這會產生這樣的id的列表：

select id 
from t 
group by id 
having SUM(case when colX = 20 then 1 else 0 end) = 0 and -- colX is never 20 
     SUM(case when colY = 31 then 1 else 0 end) = 0  -- colY is never 31 

您可以使用子查詢數數：

select count(*) 
from (select id 
     from t 
     group by id 
     having SUM(case when colX = 20 then 1 else 0 end) = 0 and -- colX is never 20 
      SUM(case when colY = 31 then 1 else 0 end) = 0  -- colY is never 31 
    ) s 

對於第二種情況，你會：

select count(*) 
from (select id 
     from t 
     group by id 
     having SUM(case when colX = 20 then 1 else 0 end) > 0 and -- colX has at least one 20 
      SUM(case when colY = 31 then 1 else 0 end) > 0  -- colY has at least one 31 
    ) s 

Answer 2

第一招：

select count(distinct id) 
from mytable 
where id not in (select id from mytable where colX = 20 or colY = 31) 

第二個：

select count(distinct id) 
from mytable t1 
join mytable t2 on t1.id = t2.id and t2.coly = 30 
where t1.colx = 20  

Answer 3

在這裏你去：

Select COUNT(distinct ID) 
from Test_Table1 A 
WHERE NOT EXISTS (SELECT 1 from Test_Table1 c 
     WHERE c.id = a.id 
     AND colX =20 AND coly= 31) 

Select COUNT(distinct ID) 
from Test_Table1 A 
WHERE EXISTS (SELECT 1 from Test_Table1 c 
     WHERE c.id = a.id 
     AND colX =20 AND coly= 31)