SQL查询具有具有两个连接关系的单独列

Question

我有一个有两个连接列的表：

外借表

id | specificmaterialinstance_id | ma​​terial_id

结果集总是在同一行中返回特定值和 generic_object

例如：使用两种材料和一种特定对象的贷款

| 211 | 3 | 4

| 211 | 3 | 20

如何在结果中有单独的对象并通过不同数量的列（2 个用于材料，1 个用于特定实例）：

| 211 | 3 |空

| 211 |空 | 4

| 211 |空 | 20

这是查询：

SELECT loan.id,
       loan.status, loan.specificmaterialinstance_id, loan.material_id

FROM (SELECT * FROM "main"."core_loan" as l 
    
     LEFT JOIN "main"."core_loan_specific_materials" as ls ON ls.loan_id = l.id
    
      LEFT JOIN "main"."core_loangenericitem" as lg ON lg.loan_id = l.id
    
     WHERE ("due_date" < date("now",'-1 day')) ) AS loan

Answer 1

试试这个

select id, specificmaterialinstance_id, NULL material_id
from loan
union all
select id, NULL, material_id 
from loan;

Answer 2

您可以将"main"."core_loan" 单独加入每个表，然后使用UNION ALL 组合结果：

SELECT l.id, ls.specificmaterialinstance_id, null material_id     
FROM "main"."core_loan" as l
LEFT JOIN "main"."core_loan_specific_materials" as ls ON ls.loan_id = l.id
WHERE (l."due_date" < date("now",'-1 day'))
UNION ALL
SELECT l.id, null, lg.material_id    
FROM "main"."core_loan" as l
LEFT JOIN "main"."core_loangenericitem" as lg ON lg.loan_id = l.id
WHERE (l."due_date" < date("now",'-1 day')) 

我假设"due_date" 是表"main"."core_loan" 中的一列。