Question

在PostgreSQL中：我有一个有3列的表：

CustomerNum, OrderNum, OrderDate。

每个日期范围内每个客户可能（或可能没有）订单很多。我需要的是每个客户的最后一个OrderNum，它位于提供的日期范围内。我一直在做的是获取客户的ResultSet并分别查询每个客户，但这需要花费太多时间。

有没有办法使用子选择来选择客户，然后获得每个客户的最后一个OrderNum？

Answer 1

在postgres上，您还可以使用非标准DISTINCT ON子句：

SELECT DISTINCT ON (CustomerNum) CustomerNum, OrderNum, OrderDate
  FROM Orders
  WHERE OrderDate BETWEEN 'yesterday' AND 'today'
  ORDER BY CustomerNum, OrderDate DESC;

请参阅http://www.postgresql.org/docs/current/static/sql-select.html#SQL-DISTINCT

Answer 2

select customernum, max(ordernum)
from table
where orderdate between '...' and '...'
group by customernum

就是这样。

Answer 3

SELECT t1.CustomerNum, t1.OrderNum As LastOrderNum, t1.LastOrderDate
  FROM table1 As t1
 WHERE t1.OrderDate = (SELECT MAX(t2.OrderDate)
                         FROM table1 t2
                        WHERE t1.CustomerNum = t2.CustomerNum
                          AND t2.OrderDate BETWEEN date1 AND date2)
   AND t1.OrderDate BETWEEN date1 AND date2

Answer 4

不确定您的Customer表的结构或关系，但这应该有效：

SELECT Customer.Num, (
    SELECT OrderNum FROM Orders WHERE CustomerNum = Customer.Num AND OrderDate BETWEEN :start AND :end ORDER BY OrderNum DESC LIMIT 1
) AS LastOrderNum
FROM Customer

Answer 5

如果按最后一个订单编号表示最大订单编号，则可以使用select作为客户编号的谓词，对结果进行分组并选择最大订单编号：

SELECT CustomerNum, MAX(OrderNum) AS LastOrderNum
    FROM Orders
    WHERE 
        CustomerNum IN (SELECT CustomerNum FROM ...)
            AND
        OrderDate BETWEEN :first_date AND :last_date
    GROUP BY CustomerNum

如果最后一个订单号不一定是最大的订单号，那么您需要找到每个客户的最大订单日期，并将其与其余订单一起加入以查找相应的订单号：

SELECT O.CustomerNum, O.OrderNum AS LastOrderNum
    FROM
        (SELECT CustomerNum, MAX(OrderDate) AS OrderDate
             FROM Orders
             WHERE
                 OrderDate BETWEEN :first_date AND :last_date
                     AND
                 CustomerNum IN (SELECT CustomerNum FROM ...)
             GROUP BY CustomerNum
        ) AS CustLatest
            INNER JOIN
        Orders AS O USING (CustomerNum, OrderDate);

Answer 6

-- generate some data
DROP TABLE tmp.orders;
CREATE TABLE tmp.orders
    ( id INTEGER NOT NULL
    , odate DATE NOT NULL
    , payload VARCHAR
    )
    ;
ALTER TABLE tmp.orders ADD PRIMARY KEY (id,odate);

INSERT INTO tmp.orders(id,odate,payload) VALUES
  (1, '2011-10-04' , 'one' )
, (1, '2011-10-24' , 'two' )
, (1, '2011-10-25' , 'three' )
, (1, '2011-10-26' , 'four' )
, (2, '2011-10-23' , 'five' )
, (2, '2011-10-24' , 'six' )
    ;

-- CTE to the rescue ...
WITH sel AS (
    SELECT * FROM tmp.orders
    WHERE odate BETWEEN '2011-10-23' AND '2011-10-24'
    )
SELECT * FROM sel s0
WHERE NOT EXISTS (
    SELECT * FROM sel sx
    WHERE sx.id = s0.id
    AND sx.odate > s0.odate
    )
    ;

结果：

DROP TABLE
CREATE TABLE
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "orders_pkey" for table "orders"
ALTER TABLE
INSERT 0 6
 id |   odate    | payload 
----+------------+---------
  1 | 2011-10-24 | two
  2 | 2011-10-24 | six
(2 rows)

PostgreSQL SELECT每个客户每个日期范围的最后一个订单

6 个答案: