MYSQL:从多个表返回多个计数而不加入

Question

accounts 表包含 account_id、account_type、date_opened。

loans 表包含 account_id、balance。

选择新贷款数量:

select count(a.account_id) from account a
    where a.date_opened > LAST_DAY(now() - INTERVAL 1 MONTH)
    and a.account_type = 'L'

选择未结贷款的数量:

select count(*) from loans l 
    where l.balance > 0

或

SUM(CASE WHEN l.balance > 0 THEN 1 ELSE 0 END) as loans_opened

如何在单个选择中执行此操作？我尝试过的事情:

select 
    count(a.account_id),
    SUM(CASE WHEN l.balance > 0 THEN 1 ELSE 0 END) as loans_opened
    from account a as new_loans,
    LEFT JOIN loans l ON l.account_id = a.account_id
    where a.date_opened > LAST_DAY(now() - INTERVAL 1 MONTH) and a.account_type = 'L'

退回 0 笔贷款

select 
    count(a.account_id) as new_loans,
    count(l.account_id) as loans_opened
    from account a as new_loans,
    LEFT JOIN loans l ON l.account_id IN (SELECT account_id from account) and balance > 0
    where a.date_opened > LAST_DAY(now() - INTERVAL 1 MONTH) and a.account_type = 'L'

查询永远不会返回

有没有办法在有或没有连接的情况下做到这一点？

Answer 1

您可以通过使用两个 SELECT 查询作为主查询的 SELECT 列表中的子查询来实现此目的:

SELECT (SELECT COUNT(*)
        FROM account
        WHERE date_opened > LAST_DAY(NOW() - INTERVAL 1 MONTH)
        AND account_type = 'L') AS new_loans,
       (SELECT COUNT(*)
        FROM loans
        WHERE balance > 0) AS open_loans;