Mysql 数据可能存在也可能不存在时联接表

让我先说我没有设计这个数据库；只是想和它一起工作

我试图检索一组自行车的故障，其中最重要的决定因素是自行车中的任何部件是否具有特定属性。该属性在零件表中设置。零件是部件的一部分，该部件具有对更大部件的引用。总成可能指定了特定的自行车类型；如果没有，则假定所有自行车类型都已指定给该部件。这些零件也可能有指定给它们的特定自行车，由序列号标识

因此，我们可以假设：

故障表中的记录将始终包括序列号、更高的总成和自行车类型

零件的部件将始终引用较高的部件

零件的总成可能有自行车类型的参考，也可能没有

零件可能有或可能没有特定序列号的参考

当搜索具有特定属性的零件的故障时，如果零件引用了特定的自行车，我们只想找到这些零件。如果没有，并且零件的装配有对特定自行车类型的引用，我们只想找到与装配相关的故障，这些装配有对这些类型的引用，并且包含这些零件。否则，我们希望找到与包含零件的较高部件相关的所有故障

我的问题是，如果我在序列号上加入，我总是只得到分配了序列号的零件，如果我在自行车类型上加入，我只得到其总成分配了类型的零件。考虑到数据库设计，我不确定我是在尝试不现实的事情，还是在错误地处理连接

以下是到目前为止的查询

SELECT f_bicycle_type, f_serial_number, f_big_assembly
FROM ( 
    SELECT DISTINCT f.f_bicycle_type, f.f_serial_number, f.f_big_assembly, p_important_attr 
    from failures f 
    left outer join (    
        select distinct bt.bt_bicycle_type, b_serial_number, a_big_assembly, p_important_attr  
        from (          
            select distinct b.b_serial_number, a.a_big_assembly, p.p_assembly_id, p.p_important_attr
            from parts p
            join assemblies a on p.p_assembly_id = a.a_assembly_id
            left outer join parts_bicycles b on b.b_part_id = p.p_id  
            where p.p_important_attr = 'awesome'
        ) p_join_a_and_b 
        left outer join assembly_bicycle_types bt on bt.bt_assembly_id = p_join_a_and_b.p_assembly_id 
    ) p_join_a_and_b_join_bt 
    on f.f_big_assembly = p_join_a_and_b_join_bt.a_big_assembly 
    -- problem join clause - if an explicit type has not been assigned to the assembly, we want to include ALL types
    and f_bicycle_type = p_join_a_and_b_join_bt.bt_bicycle_type
    -- problem join clause - there may not be explicit serial numbers assigned to a given part
    and f_serial_number = b_serial_number
) z
WHERE p_important_attr = 'awesome';

测试用例sql（针对Oracle）：

对于MySQL：

 CREATE TABLE failures (
f_bicycle_type VARCHAR(20),
f_serial_number INTEGER(20),
f_big_assembly VARCHAR(5));
CREATE TABLE parts(
p_id INTEGER( 20 ) ,
p_assembly_id INTEGER( 20 ) ,
p_important_attr VARCHAR( 20 )
);
CREATE TABLE assemblies(
a_assembly_id INTEGER( 20 ) ,
a_big_assembly VARCHAR( 5 )
);
CREATE TABLE parts_bicycles(
b_part_id INTEGER( 20 ) ,
b_serial_number INTEGER( 20 )
);
CREATE TABLE assembly_bicycle_types(
bt_assembly_id INTEGER( 20 ) ,
bt_bicycle_type VARCHAR( 20 )
);

INSERT INTO failures (f_bicycle_type, f_serial_number, f_big_assembly)
VALUES ('tandem', 1000001, 'A1000'),('bmx', 1000002, 'A1000'), ('tandem', 1000003, 'B1000'),    ('cruiser', 1000004, 'B1000') ,('bmx', 1000005, 'C1000'), ('motocross', 1000006, 'C1000')
,('cruiser', 1000007, 'C1000')
,('bmx', 1000008, 'D1000')
,('bmx', 1000009, 'D1000')
, ('cruiser', 1000010, 'E1000');
insert INTO parts (p_id, p_assembly_id, p_important_attr)
VALUES (1, 1001, 'awesome'), (2, 1001, 'ordinary'), (3, 2001, 'awesome'), (4, 3001, 'awesome'), (5, 4001, 'awesome'),(6, 5001, 'ordinary');
INSERT INTO assemblies (a_assembly_id, a_big_assembly)
VALUES (1001, 'A1000'), (2001, 'B1000'), (3001, 'C1000'), (4001, 'D1000'),(5001, 'E1000');
    INSERT INTO parts_bicycles (b_part_id, b_serial_number)
VALUES (4, 1000005),(4, 1000006),(5, 1000008)
INSERT INTO assembly_bicycle_types (bt_assembly_id, bt_bicycle_type)
VALUES (02001, 'tandem'), (04001, 'bmx');

样本数据和预期结果：

-- failures table
-- f_bicycle_type   || f_serial_number  || f_big_assembly
---------------------------------------------------------
  tandem               1000001             A1000
  bmx                  1000002             A1000
  tandem               1000003             B1000
  cruiser              1000004             B1000
  bmx                  1000005             C1000
  motocross            1000006             C1000
  cruiser              1000007             C1000
  bmx                  1000008             D1000
  bmx                  1000009             D1000
  cruiser              1000010             E1000

  -- parts table
  -- p_id   || p_assembly_id    || p_important_attr
  ------------------------------------------------
     1          1001                awesome
     2          1001                ordinary
     3          2001                awesome
     4          3001                awesome
     5          4001                awesome
     6          5001                ordinary

  -- assemblies table
  -- a_assembly_id  || a_big_assembly
  -----------------------------------
     1001              A1000
     2001              B1000
     3001              C1000
     4001              D1000
     5001              E1000

  -- parts_bicycles table
  -- b_part_id  || b_serial_number
  --------------------------------
     4              1000005
     4              1000006
     5              1000008

  -- assembly_bicycle_types table
  -- bt_assembly_id || bt_bicycle_type
  ------------------------------------
     02001             tandem
     04001             bmx

-- desired results from failures table
-- f_bicycle_type   || f_serial_number  || f_big_assembly
---------------------------------------------------------
  tandem               1000001             A1000
  bmx                  1000002             A1000
  tandem               1000003             B1000
  bmx                  1000005             C1000
      motocross            1000006             C1000
  bmx                  1000008             D1000

在问题解决后的实际结果是：

-- actual results from failures table
-- f_bicycle_type   || f_serial_number  || f_big_assembly
---------------------------------------------------------
  bmx                  1000008             D1000

---

此查询联接零件、零件、自行车、部件、部件、自行车类型。让我们将其另存为视图：

create view j_parts as
select p_important_attr, b_serial_number, a_big_assembly, bt_bicycle_type
from
  parts left join parts_bicycles
    on parts.p_id = parts_bicycles.b_part_id
  left join assemblies
    on parts.p_assembly_id=assemblies.a_assembly_id
  left join assembly_bicycle_types
    on assemblies.a_assembly_id =assembly_bicycle_types.bt_assembly_id

这（我想！）是一个查询，它给出了您想要的结果：

SELECT failures.*
FROM
  failures inner join j_parts
  on f_serial_number=b_serial_number
     and p_important_attr = 'awesome'
UNION
SELECT failures.*
FROM
  failures inner join j_parts
  on f_big_assembly=a_big_assembly
     and b_serial_number is null
     and j_parts.bt_bicycle_type=f_bicycle_type
     and p_important_attr = 'awesome'
UNION
SELECT failures.*
FROM
  failures inner join j_parts
  on f_big_assembly=a_big_assembly
     and b_serial_number is null
     and j_parts.bt_bicycle_type is null
     and p_important_attr = 'awesome'

编辑：我想这样写，因为它更容易阅读和保存。然后可以优化查询。这里有一个选择中的所有条件：

SELECT failures.*
FROM
  failures inner join
  (parts left join parts_bicycles
   on parts.p_id = parts_bicycles.b_part_id
   left join assemblies
   on parts.p_assembly_id=assemblies.a_assembly_id
   left join assembly_bicycle_types
   on assemblies.a_assembly_id =assembly_bicycle_types.bt_assembly_id)
  on f_serial_number=b_serial_number
     or (f_big_assembly=a_big_assembly
         and b_serial_number is null
         and (bt_bicycle_type=f_bicycle_type
              or bt_bicycle_type is null))
  and p_important_attr = 'awesome'

---

以下查询返回所需的结果集。从本质上说，这首先建立零件、组件和自行车类型之间的关系，然后执行复杂的、按优先级连接到故障以获得实际结果

SELECT DISTINCT f.f_bicycle_type, f.f_serial_number, f.f_big_assembly
FROM  parts p
      LEFT JOIN parts_bicycles pb
         ON p.p_id = pb.b_part_id
      LEFT JOIN assemblies a
         ON p.p_assembly_id = a.a_assembly_id
      LEFT JOIN assembly_bicycle_types abt
         ON a.a_assembly_id = abt.bt_assembly_id
      LEFT JOIN failures f
         ON -- First priority is parts that map directly
            pb.b_serial_number = f.f_serial_number 
            -- Second priority is assemblies that map to type
            OR (pb.b_serial_number IS NULL 
                AND abt.bt_bicycle_type = f.f_bicycle_type) 
            -- Third priority is assemblies that map directly
            OR (pb.b_serial_number IS NULL 
                AND abt.bt_bicycle_type IS NULL 
                AND a.a_big_assembly = f.f_big_assembly)
WHERE  p.p_important_attr = 'awesome'
ORDER BY f.f_serial_number  

我认为这并不能解决未分配的总成属于所有自行车的问题，但从您的示例数据中不清楚这是如何工作的。

好了（PostgreSQL风格）：

如果存在重复问题，请随意添加外部

选择DISTINCT*FROM

。

可以修改查询

SELECT f_bicycle_type, f_serial_number, f_big_assembly
FROM ( 
SELECT DISTINCT f.f_bicycle_type, f.f_serial_number, f.f_big_assembly, p_important_attr 
from failures f 
left outer join (    
    select distinct bt.bt_bicycle_type, b_serial_number, a_big_assembly, p_important_attr  
    from (          
        select distinct b.b_serial_number, a.a_big_assembly, p.p_assembly_id, p.p_important_attr
        from parts p
        join assemblies a on p.p_assembly_id = a.a_assembly_id
        left outer join parts_bicycles b on b.b_part_id = p.p_id  
        where p.p_important_attr = 'awesome'
    ) p_join_a_and_b 
    left join assembly_bicycle_types bt on bt.bt_assembly_id = p_join_a_and_b.p_assembly_id 
) p_join_a_and_b_join_bt 
on f.f_big_assembly = p_join_a_and_b_join_bt.a_big_assembly 
-- problem join clause - if an explicit type has not been assigned to the assembly, we want to include ALL types
and (f_bicycle_type = p_join_a_and_b_join_bt.bt_bicycle_type or p_join_a_and_b_join_bt.bt_bicycle_type is null)
-- problem join clause - there may not be explicit serial numbers assigned to a given part
and (f_serial_number = b_serial_number or b_serial_number is null)
) z
WHERE p_important_attr = 'awesome';

---

程序集可能是递归的吗？如果是，当没有“父”总成时，是否决定“分配给所有自行车类型”？另外，我们能看看你的桌子布局吗？可能还有一些样本数据和期望的结果？@Clockwork，不是递归的。不幸的是，类型的确定要么是通过在组装\自行车\类型（指所有可能的自行车类型）中缺少记录，要么是通过存在记录。我知道这不是最优的，但系统架构师不让我改变它。在假期结束之前，您可能无法提供示例数据/所需结果。我认为，如果没有嵌套，或者嵌套被分解为公共表表达式（带子句），您的查询将更容易理解其中至少可以从CTE的名称推断出每个块的含义。我不能理解你，因为我的英语很差，所以我只给你这个接近但不只是你的要求：）注意

或。。。在连接+1上为null，用于提供测试数据和创建表语句。可能还有一些问题需要解决。。。但是使用这种结构应该不会太困难……选择*是一种糟糕的做法，尤其是在有连接且数据会重复的视图中。请不要再使用它或建议使用SQL反模式。我很喜欢你关于使用工会的想法。@HLGEM你是对的。。。现在在视图中，我只选择我们在联合查询中需要的字段。。。谢谢你的建议@费希拉，我也喜欢你用工会的想法。不幸的是，从第一个查询中的所有事件中删除“and p_important_attribute='awesome'”子句并不会得到预期的结果——在这种情况下，应该返回failures表中的所有值，但缺少4、7和9。现在将查看查询#2。@earachefl第二个查询与第一个查询相同，但我用或替换了连接。。。使用联合的查询可以优化一点（不是每个选择都需要所有连接），但第二个应该更快，但除此之外。。。我不知道为什么4,7和9应该被退回。。。我还在想如果我能解决这个问题。。。
WITH chosen_parts AS (
  SELECT * FROM parts LEFT JOIN parts_bicycles ON b_part_id = p_id 
    WHERE p_important_attr = 'awesome'
), chosen_assemblies AS (
  SELECT * FROM assemblies JOIN chosen_parts ON p_assembly_id = a_assembly_id 
    LEFT JOIN assembly_bicycle_types ON bt_assembly_id = a_assembly_id 
  WHERE b_serial_number IS NULL
)
SELECT failures.* FROM chosen_parts JOIN failures 
  ON f_serial_number = b_serial_number
UNION
SELECT failures.* FROM chosen_assemblies JOIN failures 
  ON f_big_assembly = a_big_assembly 
  WHERE bt_bicycle_type = f_bicycle_type
    OR bt_bicycle_type IS NULL;

SELECT f_bicycle_type, f_serial_number, f_big_assembly
FROM ( 
SELECT DISTINCT f.f_bicycle_type, f.f_serial_number, f.f_big_assembly, p_important_attr 
from failures f 
left outer join (    
    select distinct bt.bt_bicycle_type, b_serial_number, a_big_assembly, p_important_attr  
    from (          
        select distinct b.b_serial_number, a.a_big_assembly, p.p_assembly_id, p.p_important_attr
        from parts p
        join assemblies a on p.p_assembly_id = a.a_assembly_id
        left outer join parts_bicycles b on b.b_part_id = p.p_id  
        where p.p_important_attr = 'awesome'
    ) p_join_a_and_b 
    left join assembly_bicycle_types bt on bt.bt_assembly_id = p_join_a_and_b.p_assembly_id 
) p_join_a_and_b_join_bt 
on f.f_big_assembly = p_join_a_and_b_join_bt.a_big_assembly 
-- problem join clause - if an explicit type has not been assigned to the assembly, we want to include ALL types
and (f_bicycle_type = p_join_a_and_b_join_bt.bt_bicycle_type or p_join_a_and_b_join_bt.bt_bicycle_type is null)
-- problem join clause - there may not be explicit serial numbers assigned to a given part
and (f_serial_number = b_serial_number or b_serial_number is null)
) z
WHERE p_important_attr = 'awesome';