Postgres的SQL - 從表3的數據加入到選擇一列

Question

我有3代表與下面的架構

Table1 - plan 
id | count 

Table2 - subscription 
id | plan_id 

Table3 - users 
id | subscription_id 

我不得不選擇從那裏它與plan.id比賽subscription.plan_id和用戶相匹配的計劃數.subscription_id與subscription.id和users.id匹配='5'

如何在此處使用JOIN？

我嘗試使用沒有JOIN如下：

SELECT count 
    FROM users, subscription, plan 
    WHERE users.id = '5' and users.subscription_id = subscription.id and subscription.plan_id = plan.id; 

Answer 1

儘量避免implicit SQL爲了保留可讀性聯接，而使用explicit連接（e.g. inner join,left join..）。

一個清潔的方法是如下：

SELECT 
    count 
FROM 
    users 
INNER JOIN subscription ON users.subscription_id = subscription.id 
INNER JOIN plan ON subscription.plan_id = plan.id 
WHERE users.id = '5' 

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Explicit vs implicit SQL joins