PostgreSQL - 使用子查询更新多个列值

Question

我需要能够使用子查询的结果更新表上的多个列.一个简单的例子如下所示 -

UPDATE table1
SET (col1, col2) =
  ((SELECT MIN (ship_charge), MAX (ship_charge) FROM orders))
WHERE col4 = 1001; 

我怎么能在PostgreSQL中做到这一点？

谢谢你的任何提示!

更新:我为使样本对我的实际用例过于简单而道歉.以下查询更准确 -

UPDATE table1
SET    (TOTAL_MIN_RATE, TOTAL_MAX_RATE) = (SELECT AVG(o.MIN_RATE), AVG(o.MAX_RATE)
                           FROM   ORDR o INNER JOIN table2 ba ON (o.PAY_ACCT_ID = ba.ACCT_ID) 
                                         INNER JOIN table3 mb ON (ba.BANK_ID = mb.BANK_ID)
                               WHERE  ba.CNTRY_ID = table1.CNTRY_ID AND 
                                              o.STUS_CD IN ('01','02','03','04','05','06') AND
                                  ((o.FRO_CRNCY_ID = table1.TO_CRNCY_ID AND o.TO_CRNCY_ID = table1.FRO_CRNCY_ID) OR
                                   (o.TO_CRNCY_ID = table1.TO_CRNCY_ID AND o.FRO_CRNCY_ID = table1.FRO_CRNCY_ID))   
                               GROUP BY ba.CNTRY_ID)

Answer 1

如果要避免两个子选择,可以像下面这样重写查询:

UPDATE table1
  SET col1 = o_min, col2 = o_max
FROM ( 
    SELECT min(ship_charge) as o_min, 
           max(ship_charge) as o_max
    FROM orders
) t 
WHERE col4 = 1001

如果ship_charge未编入索引,则应该比两个子选择更快.如果ship_charge被编入索引,则可能没有太大的区别

编辑

从Postgres 9.5开始,这也可以写成:

UPDATE table1
  SET (col1, col2) = (SELECT min(ship_charge), max(ship_charge) FROM orders)
WHERE col4 = 1001

Answer 2

UPDATE table1
SET
    col1 = subquery.min_value,
    col2 = subquery.max_value
FROM
(

    SELECT
        1001 AS col4,
        MIN (ship_charge) AS min_value,
        MAX (ship_charge) AS max_value
    FROM orders
) AS subquery
WHERE table1.col4 = subquery.col4

如果要在table1中一次更新多行,也可以在子查询中返回多行.

Answer 3

这不是最有效的方法,但它很简单:

UPDATE table1 SET
col1 = (SELECT MIN (ship_charge) FROM orders),
col2 = (SELECT MAX (ship_charge) FROM orders)
WHERE col4 = 1001; 

Answer 4

一个选项(但不是唯一的选项)是使用两个单独的子查询:

update table1
set col1 = (select min(ship_charge) from orders),
    col2 = (select max(ship_charge) from orders)
where col4 = 1001;

从PostgreSQL 9.0的更新精细手册:

根据标准,列列表语法应允许从单个行值表达式分配列的列表,例如子选择:

UPDATE accounts SET (contact_last_name, contact_first_name) =
(SELECT last_name, first_name FROM salesmen
 WHERE salesmen.id = accounts.sales_id);

目前尚未实现 - 源必须是独立表达式列表.