Sql 从多个表中获取组合行

我有一个主表和一些子表，它们至少包含主表中的一列。子表是主表某些部分的更新。我想在特定日期更新主表的行

Main table:

table1
| id | colA | colB | colC | colD | colE | createDate  |
|:---|:----:|:----:|:----:|:----:|:----:|:-----------:|
| a1 |  1   |  1   |  1   |  1   |  1   |  2017/01/01 |

Sub-tables :

table2
| mainid | colA | colB | createdate  |
|:------:|:----:|:----:|:-----------:|
|   a1   |  2   |  2   |  2018/05/01 |
|   a1   |  3   |  3   |  2019/01/01 |
|   a1   |  4   |  4   |  2020/01/01 |

table3
| mainid | colA | colB | colC | createDate  |
|:------:|:----:|:----:|:----:|:-----------:|
|   a1   |  6   |  6   |  6   |  2019/01/01 |
|   a1   |  7   |  7   |  7   |  2020/01/01 |
|   a1   |  8   |  8   |  8   |  2021/01/01 |

table4
| mainid | colA | colE | colC | createDate  |
|:------:|:----:|:----:|:----:|:-----------:|
|   a1   |  9   |  9   |  9   |  2018/06/01 |
|   a1   |  10  |  10  |  10  |  2017/01/01 |
|   a1   |  12  |  12  |  12  |  2020/01/01 |

我通过以下代码从每个表中获取行：

select * from table2 where createDate < '2018-07-01' and mainid='a1' order by createDate desc limit 1;
select * from table3 where createDate < '2018-07-01' and mainid='a1' order by createDate desc limit 1;
select * from table4 where createDate < '2018-07-01' and mainid='a1 'order by createDate desc limit 1;

select * from table1 where id = 'a1'; 

---

如何在一个查询中完成此操作？这可能吗？我应该用另一种方式尝试吗？

假设所有列都不为空，否则您将不得不做更多的工作

首先，您可以合并列出的所有查询，并为缺少的列填写空值，以获得兼容的行类型。然后加总。剩余的困难是，该任务的完美聚合函数没有在库存Postgres中实现

使用标准的库存SQL工具 然后：

使用由提供的C实现更快

小提琴

相关，包含更多详细信息和选项：

---

假设所有列都不为NULL，否则您将不得不执行更多操作

首先，您可以合并列出的所有查询，并为缺少的列填写空值，以获得兼容的行类型。然后加总。剩余的困难是，该任务的完美聚合函数没有在库存Postgres中实现

使用标准的库存SQL工具 然后：

使用由提供的C实现更快

小提琴

相关，包含更多详细信息和选项：

---

对于这种情况，您应该使用sql连接。如果您提供了一个FIDLE或实际的CREATE TABLE和INSERT语句，这将使我们更加容易。当然，永远都是你的博士后版本。对不起，我以后会处理的对于这种情况，您应该使用sql连接。如果您提供了一个FIDLE或实际的CREATE TABLE和INSERT语句，这将使我们更加容易。当然，永远都是你的博士后版本。对不起，我以后会处理的非常感谢你。你帮了我很多。我不知道该说什么你太棒了！非常感谢你。你帮了我很多。我不知道该说什么你太棒了！

table1 -> colD: 1
table2 -> colB: 2
table3 -> nothing
table4 -> colA: 9, colC: 9, colE: 9

 selected row :
| id | colA | colB | colC | colD | colE |filteredDate |
|:---|:----:|:----:|:----:|:----:|:----:|:-----------:|
| a1 |  9   |  2   |  9   |  1   |  9   |  2018/07/01 |

SELECT id
    , (array_agg(colA ORDER BY colA IS NULL, createDate DESC))[1] AS colA
    , (array_agg(colB ORDER BY colB IS NULL, createDate DESC))[1] AS colB
    , (array_agg(colC ORDER BY colC IS NULL, createDate DESC))[1] AS colC
    , (array_agg(colD ORDER BY colD IS NULL, createDate DESC))[1] AS colD
    , (array_agg(colE ORDER BY colE IS NULL, createDate DESC))[1] AS colE
FROM (
   select      id, colA, colB, colC, colD, colE, createDate from table1 where id = 'a1'
   UNION ALL
   (select mainid, colA, colB, NULL, NULL, NULL, createDate from table2 where createDate < '2018-07-01' and mainid='a1' order by createDate desc limit 1)
   UNION ALL
   (select mainid, colA, colB, colC, NULL, NULL, createDate from table3 where createDate < '2018-07-01' and mainid='a1' order by createDate desc limit 1)
   UNION ALL
   (select mainid, colA, NULL, colc, NULL, colE, createDate from table4 where createDate < '2018-07-01' and mainid='a1' order by createDate desc limit 1)
   ) sub
GROUP BY 1;

CREATE OR REPLACE FUNCTION first_agg ( anyelement, anyelement )
RETURNS anyelement LANGUAGE SQL IMMUTABLE STRICT AS 'SELECT $1';
 
CREATE AGGREGATE FIRST (
        sfunc    = first_agg,
        basetype = anyelement,
        stype    = anyelement
);

SELECT id
     , first(colA) AS colA
     , first(colB) AS colB
     , first(colC) AS colC
     , first(colD) AS colD
     , first(colE) AS colE
FROM (
   SELECT      id, colA, colB, colC, colD, colE, createDate FROM table1 WHERE     id='a1'
   UNION ALL
   (SELECT mainid, colA, colB, NULL, NULL, NULL, createDate FROM table2 WHERE mainid='a1' AND createDate < '2018-07-01' ORDER BY createDate DESC LIMIT 1)
   UNION ALL
   (SELECT mainid, colA, colB, colC, NULL, NULL, createDate FROM table3 WHERE mainid='a1' AND createDate < '2018-07-01' ORDER BY createDate DESC LIMIT 1)
   UNION ALL
   (SELECT mainid, colA, NULL, colc, NULL, colE, createDate FROM table4 WHERE mainid='a1' AND createDate < '2018-07-01' ORDER BY createDate DESC LIMIT 1)
   ORDER BY createDate DESC
   ) sub
GROUP  BY 1;