Sql 从两个表中获取第一条记录

我希望从下面的示例表中获得客户的第一个日期和项目描述

创建我的示例

CREATE TABLE cust
(
CUSTNO int,
ENAME varchar(50)
)

CREATE TABLE orders
(
CUSTNO int,
Description varchar(50),
ORDERDATE date
)

INSERT INTO cust VALUES (7369, 'SMITH');
INSERT INTO cust VALUES (7499, 'ALLEN');
INSERT INTO cust VALUES (7521, 'WARD');
INSERT INTO cust VALUES (7566, 'JONES');
INSERT INTO cust VALUES (7654, 'MARTIN');
INSERT INTO cust VALUES (7698, 'BLAKE');
INSERT INTO cust VALUES (7782, 'CLARK');
INSERT INTO cust VALUES (7788, 'SCOTT');
INSERT INTO cust VALUES (7839, 'KING');
INSERT INTO cust VALUES (7844, 'TURNER');
INSERT INTO cust VALUES (7876, 'ADAMS');
INSERT INTO cust VALUES (7900, 'JAMES');
INSERT INTO cust VALUES (7902, 'FORD');
INSERT INTO cust VALUES (7934, 'MILLER');

INSERT INTO orders VALUES (7782, 'Something','17-DEC-1980');
INSERT INTO orders VALUES (7782, 'Something else', '17-DEC-2000');
INSERT INTO orders VALUES (7900, 'Something', '17-DEC-1980');
INSERT INTO orders VALUES (7900, 'Something else','17-DEC-1990');
INSERT INTO orders VALUES (7934, 'Something','17-DEC-1980');

我在尝试这样的事情

  select [ENAME],[cust].[CUSTNO], MIN([ORDERDATE]),[Description]
  from [cust],[orders]
  where [cust].[CUSTNO]=[orders].[CUSTNO]
  group by [cust].[CUSTNO],[ENAME],[Description]

我的问题是返回的行太多。我只想看到每个客户，然后列出他们的第一个日期（如果没有订单，则为空或空）

---

有什么想法吗？

只需从

分组依据

子句中省略

[ENAME]

和

[Description]

，

只需从
分组依据
子句中省略
[ENAME]
和
[Description]

;with cteMinOrder as (
    select [CUSTNO], MIN([ORDERDATE]) as minDate
        from [orders]
        group by [CUSTNO]
)
select [ENAME],[cust].[CUSTNO], mo.minDate, [Description]
    from [cust]
        left join cteMinOrder mo
            on [cust].[CUSTNO]=mo.[CUSTNO]
        left join [orders]
            on [cust].[CUSTNO]=[orders].[CUSTNO]
                and mo.minDate = [orders].[ORDERDATE]

 with MinOrder as (
  select
  custno, min(orderdate) orderdate
  from [orders]
  GROUP BY custno)

  select [ENAME],[cust].[CUSTNO], o.[orderdate], [Description]
   from 
  cust 
  LEFT JOIN orders o
  ON cust.custNo = o.custno
  LEFT JOiN MinOrder mo
  ON mo.orderdate = o.orderdate
    and mo.custno = o.custno

如果不能使用CTE，则可以使用内联视图

 select [ENAME],[cust].[CUSTNO], o.[orderdate], [Description]
   from 
  cust 
  LEFT JOIN orders o
  ON cust.custNo = o.custno
  LEFT JOiN (  select
     custno, min(orderdate) orderdate
  from [orders]
  GROUP BY custno)  mo
  ON mo.orderdate = o.orderdate
    and mo.custno = o.custno

如果不能使用CTE，则可以使用内联视图

 select [ENAME],[cust].[CUSTNO], o.[orderdate], [Description]
   from 
  cust 
  LEFT JOIN orders o
  ON cust.custNo = o.custno
  LEFT JOiN (  select
     custno, min(orderdate) orderdate
  from [orders]
  GROUP BY custno)  mo
  ON mo.orderdate = o.orderdate
    and mo.custno = o.custno

语法可能需要根据您使用的实际方言进行调整，但这种关系应该满足您的需要

  SELECT c.[ENAME],c.[CUSTNO], o.[orderdate], o.[Description] 
   FROM  cust  c
  LEFT JOIN orders o 
    ON c.custNo = o.custno 
  LEFT JOIN 
        ( SELECT   custno, min(orderdate) orderdate 
            FROM [orders] 
            GROUP BY custno)  mo 
    ON mo.orderdate = o.orderdate 
        AND mo.custno = o.custno 

语法可能需要根据您使用的实际方言进行调整，但这种关系应该满足您的需要

  SELECT c.[ENAME],c.[CUSTNO], o.[orderdate], o.[Description] 
   FROM  cust  c
  LEFT JOIN orders o 
    ON c.custNo = o.custno 
  LEFT JOIN 
        ( SELECT   custno, min(orderdate) orderdate 
            FROM [orders] 
            GROUP BY custno)  mo 
    ON mo.orderdate = o.orderdate 
        AND mo.custno = o.custno 

如果存在订单，则需要左连接来获取订单；如果不存在订单，则仍然需要左连接来获取客户@conrad Frix的解决方案也会起作用，但我在使用不接受with语句的数据库时考虑了这一点

将来，您应该停止编写隐式联接（使用逗号分隔表并将联接条件放入where子句）。它们是一种糟糕的编程技术，并导致您无法正确理解联接（或者您可能知道使用左联接）

如果存在订单，则需要左连接来获取订单；如果不存在订单，则仍然需要左连接来获取客户@conrad Frix的解决方案也会起作用，但我在使用不接受with语句的数据库时考虑了这一点

将来，您应该停止编写隐式联接（使用逗号分隔表并将联接条件放入where子句）。它们是一种糟糕的编程技术，并导致您无法正确理解联接（或者您可能知道使用左联接）
 @HGLEM我想你是对的@HGLEM我想你是对的