Question

我有3个表格，如下所示，我想连接在一起，以便属性表的行成为结果表的列。

block
id  name
1   a
2   b
3   c
4   d

attr_value
id   value  block_id attr_type_id
1    0.1    1         1
2    0.2    1         2
3    0.3    2         3
4    0.4    3         4

attr_type
id   name
1    type_a
2    type_b
3    type_c
4    type_d


result table
block id  name   type_a  type_b  type_c  type_d 
1         a      0.1     0.2     null    null
2         b      null    null    0.3     null
3         c      null    null    null    0.4
4         d      null    null    null    null

我正在使用postgresql并尝试case when，但这会复制一些列（即id = 1的多个块行），这是我不想要的。

Answer 1

select  b.id,b.name
,(select a.value from attr_value a inner join attr_type at on at.id=a.attr_type_id where b.id=a.block_id and at.id=1) as 'type_a'
,(select a.value from attr_value a inner join attr_type at on at.id=a.attr_type_id where b.id=a.block_id and at.id=2) as 'type_b'
,(select a.value from attr_value a inner join attr_type at on at.id=a.attr_type_id where b.id=a.block_id and at.id=3) as 'type_c'
,(select a.value from attr_value a inner join attr_type at on at.id=a.attr_type_id where b.id=a.block_id and at.id=4) as 'type_d'
from block b

Answer 2

CREATE TEMPORARY TABLE result_table
(
    blockid bigint,
    name varchar(10),
    type_a float default 1,
    type_b float default 2,
    type_c float default 3,
    type_d float default 4
)

insert into result_table(blockid,name)select id,name from block

update result_table
set type_a=(select value from attr_values a where a.block_id=blockid and a.attr_type_id=type_a)
,type_b=(select value from attr_values a where a.block_id=blockid and a.attr_type_id=type_b)
,type_c=(select value from attr_values a where a.block_id=blockid and a.attr_type_id=type_c)
,type_d=(select value from attr_values a where a.block_id=blockid and a.attr_type_id=type_d)


select * from result_table

drop table result_table

将行连接到列中

2 个答案: