Question

我一直在提高我的SQL知识，但仍然无法理解如何创建一些查询。

我在SQL Server数据库中有以下表格：

用户（ID，姓名）

贷款（id_sender，id_receiver，金额，日期，日期_付款）

什么是有效查询：

选择在2014年和2015年向其他用户发送贷款的用户的姓名
选择已向对方发送贷款的用户的对（id1，id2）

非常感谢任何建议！

编辑1：

我的尝试：

1

SELECT name FROM User WHERE id IN (
    SELECT id_sender FROM Loan WHERE
    id_receiver IN (SELECT DISTINCT id_receiver WHERE YEAR(date) = 2014) AND
    id_receiver IN (SELECT DISTINCT id_receiver WHERE YEAR(date) = 2015)
)

2

SELECT id1, id2 FROM (
    SELECT DISTINCT id_sender as id1 FROM Loan
    WHERE id_receiver IN (
        SELECT DISTINCT id_sender FROM Loan
        WHERE id_receiver = ???
    )
    (?)
)

Answer 1

示例1：如果您的date列有索引，最好不要在列周围使用函数，这样您就可以实际使用索引。

SELECT name
FROM User
WHERE id IN (SELECT id_sender FROM Loan WHERE date >= '1/1/2014' AND date < '1/1/2015')
    AND id IN (SELECT id_sender FROM Loan WHERE date >= '1/1/2015' AND date < '1/1/2016')

示例2：您可以使用自联接仅使用贷款表来查找匹配项。

SELECT
    L1.id_sender AS id1,
    L1.id_receiver AS id2
FROM Loan L1
    INNER JOIN Loan L2
        ON L1.id_sender = L2.id_receiver
            AND L2.id_sender = L1.id_receiver

Answer 2

1

SELECT name
FROM user
WHERE id EXISTS (
  Select Distinct id_sender 
  FROM loan 
  WHERE year(date) between 2014 and 2015
)

2

SELECT s.id1,s.id2, s.monto, p.nombre
FROM sap s INNER JOIN sop p
ON s.id1 = p.id_comun INNER JOIN sap a
ON a.id2 = p.id_comun
UNION
SELECT s.id1,s.id2, s.monto, p.nombre
FROM sap s INNER JOIN sop p
ON s.id1 = p.id_comun INNER JOIN sap a
ON a.id2 = p.id_comun

从数据库中选择相关记录

2 个答案: