Question

我是SQL的新手，我在这里有一个问题。我在Postgresql工作。我的表看起来像

更改

     id action_id(fk)   field_id(fk)    old_value   new_value   
------------------------------------------------------------------
      39      15              14                           testPool
      40      15              15                           testSystem 
      41      15              16                           61019

动作

     id  description       audited_table     audited_row      audited_type  
-----------------------------------------------------------------------------
     15  Added system       systemtable        61019          insert

字段

      id       audited_table                name    
---------------------------------------------------------------------------
      14       systemtable                 pool
      15       systemtable                 storagesystem
      15       systemtable                 id

我想写一个查询来获取以下视图

  id        description                  audited_table               audited_row      audited_type   field.name1     name1->new_value  field.name2     name2->new_value
-----------------------------------------------------------------------------------------------------------------------------------------------------------
  15        Added system                 systemtable                 61019              insert         pool            testPool        storagesystem    testSystem

基本上我想将（更改行）列展平（行），并将其与'action'表连接起来。请注意'更改'表引用'action'和'field'表

架构图如下所示

感谢任何帮助，谢谢

enter image description here

Answer 1

实际上并不完全清楚你所追求的是什么，但让我尝试回答。

首先让我们创建表格和示例数据：

SQL Fiddle

PostgreSQL 9.1.9架构设置：

CREATE TABLE Change
    ("id" int, "action_id" int, "field_id" int, "old_value" varchar(10), "new_value" varchar(10))
;

INSERT INTO Change
    ("id", "action_id", "field_id", "old_value", "new_value")
VALUES
    (39, 15, 14,'', 'testPool'),
    (40, 15, 15,'', 'testSystem'),
    (41, 15, 16,'', '61019')
;

CREATE TABLE Action
    ("id" int, "description" varchar(12), "audited_table" varchar(11), "audited_row" int, "audited_type" varchar(6))
;

INSERT INTO Action
    ("id", "description", "audited_table", "audited_row", "audited_type")
VALUES
    (15, 'Added system', 'systemtable', 61019, 'insert')
;

CREATE TABLE Field
    ("id" int, "audited_table" varchar(11), "name" varchar(13))
;

INSERT INTO Field
    ("id", "audited_table", "name")
VALUES
    (14, 'systemtable', 'pool'),
    (15, 'systemtable', 'storagesystem'),
    (15, 'systemtable', 'id')
;

如果您的问题是关于如何加入表格，答案是相当直接的：

查询1 ：

SELECT C.id,
       A.description,
       F.audited_table,
       A.audited_row,
       A.audited_type,
       F.name AS field_name,
       C.new_value
  FROM Change AS C
  JOIN Action AS A
    ON C.action_id = A.id
  JOIN Field AS F
    ON C.field_id = F.id;

<强> Results ：

| ID |  DESCRIPTION | AUDITED_TABLE | AUDITED_ROW | AUDITED_TYPE |    FIELD_NAME |  NEW_VALUE |
|----|--------------|---------------|-------------|--------------|---------------|------------|
| 39 | Added system |   systemtable |       61019 |       insert |          pool |   testPool |
| 40 | Added system |   systemtable |       61019 |       insert | storagesystem | testSystem |
| 40 | Added system |   systemtable |       61019 |       insert |            id | testSystem |

有关联接的详细信息，请查看我的博客系列：sqlity.net/en/1146/a-join-a-day-introduction/ 它基于SQL Server，但大部分信息都与您使用的RDBMS无关。

如果您想将多行变成一行，那么您正在寻找一个支点。您可以通过将行组合在一起，然后使用MAX()和CASE的组合来选择单个值来执行数据透视表。您的问题的问题是您没有指定字段“field1”与“field2”的对应关系。为了解决这个问题，我使用ROW_NUMBER()函数按字段id的顺序在字段中添加了编号。使用它，第一个字段是具有最小field_id的字段。枢轴现在看起来像这样：

查询2 ：

SELECT action_id,
       audited_table,
       MAX(CASE WHEN field_number = 1 THEN name END) AS f1_name,
       MAX(CASE WHEN field_number = 1 THEN new_value END) AS f1_new_value,
       MAX(CASE WHEN field_number = 2 THEN name END) AS f2_name,
       MAX(CASE WHEN field_number = 2 THEN new_value END) AS f2_new_value
  FROM(
    SELECT *,ROW_NUMBER()OVER(PARTITION BY C.action_id, F.audited_table ORDER BY F.id) field_number
      FROM Change AS C
      JOIN Field AS F
        ON C.field_id = F.id
    )X
 GROUP BY action_id, audited_table;

<强> Results ：

| ACTION_ID | AUDITED_TABLE | F1_NAME | F1_NEW_VALUE | F2_NAME | F2_NEW_VALUE |
|-----------|---------------|---------|--------------|---------|--------------|
|        15 |   systemtable |    pool |     testPool |      id |   testSystem |

查询2只获取Field和Change表的信息。要获取Action信息，我们还需要添加另一个连接：

查询3 ：

SELECT A.id,
       A.description,
       X2.audited_table,
       A.audited_row,
       A.audited_type,
       X2.f1_name,
       X2.f1_new_value,
       X2.f2_name,
       X2.f2_new_value
  FROM Action AS A
  JOIN (
    SELECT action_id,
           audited_table,
           MAX(CASE WHEN field_number = 1 THEN name END) AS f1_name,
           MAX(CASE WHEN field_number = 1 THEN new_value END) AS f1_new_value,
           MAX(CASE WHEN field_number = 2 THEN name END) AS f2_name,
           MAX(CASE WHEN field_number = 2 THEN new_value END) AS f2_new_value
      FROM(
        SELECT *,ROW_NUMBER()OVER(PARTITION BY C.action_id, F.audited_table ORDER BY F.id) field_number
          FROM Change AS C
          JOIN Field AS F
            ON C.field_id = F.id
        )X1
     GROUP BY action_id, audited_table
  )X2  
  ON A.id = X2.action_id

<强> Results ：

| ID |  DESCRIPTION | AUDITED_TABLE | AUDITED_ROW | AUDITED_TYPE | F1_NAME | F1_NEW_VALUE | F2_NAME | F2_NEW_VALUE |
|----|--------------|---------------|-------------|--------------|---------|--------------|---------|--------------|
| 15 | Added system |   systemtable |       61019 |       insert |    pool |     testPool |      id |   testSystem |

我希望这能回答你的问题。

加入表（SQL）

1 个答案: