sql - 如何更好的优化SQL查询？

Question

我写了请求，但我担心它可能非常未优化，我会遇到问题。

任务:查找没有债务且上次付款时间超过 2 年的用户。没有任何订单的不必要的用户

我们有两个表:

 User tbl (Id (int), LastName (string))

 Order tbl (Id (int), UserId (int), IsPaid (bool), DatePaid (Date, not null))

I wrote a Sql request, but I'm afraid I'm down with 20k of users and lots of orders

I have found all those who have no debts and the last payment is for a period of two years. Now I want to remove them from the general list and so users who need me remain.
It seems bad idea

SELECT u."Id"
FROM "User" AS u
LEFT JOIN
   (SELECT *
    FROM "Order"
    WHERE "UserId" IN
       (SELECT "Id"
        FROM "User"
        WHERE "Id" NOT IN
           (SELECT DISTINCT "UserId"
            FROM "Order"
            WHERE "IsPaid" IS FALSE )
       )
    AND "DatePaid" > '2016-10-10'
   ) AS p
   ON p."UserId" = u."Id";

Answer 1

我想你只是想要这样的东西:

select o.userid
from orders o
group by o.userid
having sum(case when o.isPaid then 1 else 0 end) = count(*) and -- all are paid
       max(o.paymentdate) < current_date - interval '2 year';

请注意，众所周知，日期函数是特定于数据库的。以上使用 ANSI/ISO 标准语法。

如果您想要有关用户的完整信息，则可以使用不同的结构:

select u.*
from users u
where not exists (select 1
                  from orders o
                  where o.userid = u.id and not u.ispaid
                 ) and
      not exists (select 1
                  from orders o
                  where o.userid = u.id and
                        u.paymentdate > current_date - interval '2 year'
                 );