如何在SQL中使用IF THEN，具體場景

Question

我當前的問題是嘗試構建一個查詢，給定一個條件它給了我一個特定的計數。

我需要提取已在我們網站上銷售商品的用戶列表，但目前沒有任何商品列出。結果應該是僅有當前未發佈項目的用戶列表。

我的查詢如下：

select `products`.`id` as 'product id', `users`.`id` as 'user id', 
`users`.`full_name` as 'user full name',`users`.`email` as 'user email' 
(CASE WHEN `products`.`is_published` = 1 
    THEN count(`products`.`ìs_published`) = 0 
    ELSE END) 
from `users`,`products` 
and `users`.`is_active` = 1 
and `products`.`user_id` = `users`.`id` 
group by `users`.`id` 
order by 'user id' asc; 

對於背景下，如果products.is_published = 1則意味着用戶有一個活項目，如果是= 0，這意味着該項目沒有公佈，因此賣家不活躍。但是，有些情況下，賣家可能有過去已售出的物品，再加上活物品，因此即使products.is_published = 0也會顯示出來，因爲它們都有。

任何幫助將不勝感激。

Answer 1

，你可以指望用戶項目中的子查詢，像這樣：

select users.id as 'user id' 
, users.full_name as 'user full name' 
, users.email as 'user email' 
, (select count(1) from products where is_published = 1 and user_id = users.id) as 'count of published' 
from users 
Where is_active = 1 
order by 'user id' asc; 

，如果你需要，只有當用戶已經發布的產品試試這個數：

select users.id as 'user id' 
, users.full_name as 'user full name' 
, users.email as 'user email' 
, pc.c as 'count of published' 
from users 
inner join (select user_id, count(1) as c from products where is_published = 1 group by user_id) as pc on pc.user_id = users.id 
Where is_active = 1 
order by 'user id' asc;