UNNEST列

Question

我有一些SQL，其具有我試圖從數據庫中列有值替換

with pre as (
with a(k, v) as (select id, my_column from mytable), 
col(s, n) as (select * from unnest(array['Title', 'First', 'Middle', 'Last']) with ordinality c (s, n)) 

我試圖像這樣的東西來代替UNNEST SQL一些硬編碼值：

select unnest(string_to_array(my_column, ':')) as elements from mytable 

mycolumn內容在長度上有所不同，但一個實例可能是標題= AAA：第一= BBB：中間= CCC：最後= DDD

由於

Answer 1

我基於我的回答on your previous post。下面是如何可以在序數加入unnest(string_to_array(my_column, ':'))名爲列的例子：

t=# with a as (select id,k,v from my_table, unnest(string_to_array(my_column, ':')) with ordinality as t(k,v)) 
, col(s, n) as (select * from unnest(array['Title', 'First', 'Middle', 'Last']) with ordinality c (s, n)) 
select * from a join col on n=v; 
id |  k  | v | s | n 
----+------------+---+--------+--- 
    1 | title=aaa | 1 | Title | 1 
    1 | first=bbb | 2 | First | 2 
    1 | middle=ccc | 3 | Middle | 3 
    1 | last=ddd | 4 | Last | 4 
(4 rows) 

當然，你將不得不加入不同（基於您以前的帖子）。但是，如果不清楚的部分是如何從表中選擇而不是從值中選擇，那麼上面的示例應該會有所幫助。

更新

認沽值表：

t=# create table keys(t text); 
CREATE TABLE 
Time: 91.908 ms 
t=# insert into keys select unnest(array['Title', 'First', 'Middle', 'Last']); 
INSERT 0 4 
Time: 11.552 ms 
t=# select * from keys ; 
    t 
-------- 
Title 
First 
Middle 
Last 
(4 rows) 

現在加入反對鍵表：

t=# with a as (select id,k,v from my_table, unnest(string_to_array(my_column, ':')) with ordinality as t(k,v)) 
select * from a join keys on split_part(k,'=',1) = lower(t); 
id |  k  | v | t 
----+------------+---+-------- 
    1 | first=bbb | 2 | First 
    1 | last=ddd | 4 | Last 
    1 | middle=ccc | 3 | Middle 
    1 | title=aaa | 1 | Title 
(4 rows)