在数据可能存在或不存在时连接表

Question

让我先说我没有设计这个数据库; 只是想尝试使用它.

我正在尝试检索一套自行车的故障,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parts表中设置.该零件是组件的一部分,该组件引用了更大的组件.组件可以具有分配给它的特定自行车类型; 如果没有,我们假设所有自行车类型都分配给组件.这些部件还可以具有分配给它们的特定自行车,由序列号标识.

所以,我们可以假设:

1. 故障表中的记录将始终包含序列号,更高的装配和自行车类型.
2. 零件的装配将始终具有对更高装配的引用
3. 零件的装配可能会也可能不会引用自行车类型.
4. 部件可能会也可能不会引用特定的序列号

当搜索存在具有特定属性的零件的故障时,如果零件具有对特定自行车的引用,我们只想找到那些.如果没有,并且零件的装配具有对特定自行车类型的引用,我们只希望找到与引用这些类型的装配相关的故障,并且包含这些部分.否则,我们希望找到与包含零件的较高装配相关的所有故障.

我的问题是,如果我加入序列号,我总是只得到分配序列号的部分,如果我加入自行车类型,我只得到其程序集分配了类型的部分.我不确定我是否正在尝试一些根据数据库设计不切实际的东西,或者我是否正在接近错误的连接.

以下是目前为止的查询.

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(适用于Oracle):

CREATE TABLE failures (
f_bicycle_type VARCHAR(20),
f_serial_number NUMBER(20),
f_big_assembly VARCHAR(5)); 

CREATE TABLE parts (
p_id NUMBER(20),
p_assembly_id NUMBER(20),
p_important_attr VARCHAR(20));

CREATE TABLE assemblies (
a_assembly_id NUMBER(20),
a_big_assembly VARCHAR(5)); 

CREATE TABLE parts_bicycles (
b_part_id NUMBER(20),
b_serial_number NUMBER(20));    

CREATE TABLE assembly_bicycle_types (
bt_assembly_id NUMBER(20),
bt_bicycle_type VARCHAR(20));

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

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');

样本数据和期望的结果:

-- 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

实际结果,问题加入到位:

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

Answer 1

此查询连接 parts、parts_bicycles、assemblies、 assembly_bicycle_type。让我们将其保存为视图：

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（我认为！）是为您提供所需结果的查询：

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维护。然后就可以优化查询了。这里只需一项选择即可包含所有条件：

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'