在另一个表中的一行的 UPDATE 中使用同一表中的多行

Question

我正在为 PostgreSQL (9.1) 使用 pgadmin，我有这个查询需要很长时间才能运行

update tableA a
set owner1_surname = (select owner_surname from owners_distinct b where a.owner1= b.owner),
owner1_othername   = (select owner_othername from owners_distinct b where a.owner1= b.owner),
owner2_surname     = (select owner_surname from owners_distinct b where a.owner2= b.owner),
owner2_othername   = (select owner_othername from owners_distinct b where a.owner2= b.owner),
owner3_surname     = (select owner_surname from owners_distinct b where a.owner3= b.owner),
owner3_othername   = (select owner_othername from owners_distinct b where a.owner3= b.owner)

不必一次又一次地从owners_distinct table 检索值，是否可以使用SELECT 检索列owner、owner_surname 和owner_othername，然后在@ 上执行UPDATE 987654328@的列基于检查？

Answer 1

这比我最初想象的要复杂，因为您想多次加入同一个表，而唯一的连接是更新后的表本身：

UPDATE table_a a
    SET owner1_surname = b1.owner_surname
    ,owner1_othername  = b1.owner_othername
    ,owner2_surname    = b2.owner_surname
    ,owner2_othername  = b2.owner_othername
    ,owner3_surname    = b3.owner_surname
    ,owner3_othername  = b3.owner_othername
FROM   table_a x
LEFT   JOIN owners_distinct b1 ON b1.b.owner = x.owner1
LEFT   JOIN owners_distinct b2 ON b2.b.owner = x.owner2 
LEFT   JOIN owners_distinct b2 ON b3.b.owner = x.owner3
WHERE  x.table_a_id = a.table_a_id

其中table_a_id 是table_a 的主键。通常您不必再次加入该表，但在这种情况下，您需要它来进行加入之前您可以链接到更新的表。

我使用LEFT JOIN，以防止在owners_distinct 中找不到三个所有者之一时对一行的整个更新失败。

数据库设计

您确定需要table_a 中的所有冗余数据吗？规范化模式中的规范方法是仅存储foreign keys（owner1、owner2、owner3），并在SELECT 中使用JOIN 按需获取名称的详细信息。完全删除您正在更新的所有列。当然，规则总是有例外的......

没有唯一键？

这不应该发生在开始。您应该添加一个代理主键，例如：

ALTER TABLE table_a ADD table_a_id serial PRIMARY KEY;

在相关答案中了解更多信息：
Do I need a primary key for my table, which has a UNIQUE (composite 4-columns), one of which can be NULL?

没有唯一键的解决方案

无论如何，这里有一种方法可以使此更新不受任何唯一列的影响：

UPDATE table_a a
    SET owner1_surname = b1.owner_surname
    ,owner1_othername  = b1.owner_othername
    ,owner2_surname    = b2.owner_surname
    ,owner2_othername  = b2.owner_othername
    ,owner3_surname    = b3.owner_surname
    ,owner3_othername  = b3.owner_othername
FROM   (SELECT DISTINCT owner1, owner2, owner3 FROM table_a) x
LEFT   JOIN owners_distinct b1 ON b1.b.owner = x.owner1
LEFT   JOIN owners_distinct b2 ON b2.b.owner = x.owner2 
LEFT   JOIN owners_distinct b2 ON b3.b.owner = x.owner3
WHERE  x.owner1 = a.owner1
AND    x.owner2 = a.owner2
AND    x.owner3 = a.owner3;

重点是：我们只需要(owner1, owner2, owner3)的每个组合一次。

Answer 2

从 table_a 中选择所有者、所有者姓氏和所有者其他名称

更新 table_a

 SET owner1_surname = b1.owner_surname
,owner1_othername  = b1.owner_othername
,owner2_surname    = b2.owner_surname
,owner2_othername  = b2.owner_othername
,owner3_surname    = b3.owner_surname
,owner3_othername  = b3.owner_othername