ROWS FROM（）中具有多个非唯一调用的列定义

Question

我想在select子句中使用多个数组。最明显的一个没有工作和PostgreSQL点ROWS FROM() ...

select * from unnest(array[1,2], array[3,4]) as (a int, b int); 

错误：

UNNEST() with multiple arguments cannot have a column definition list 
LINE 1: select * from unnest(array[1,2], array[3,4]) as (a int, b in... 
                 ^
HINT: Use separate UNNEST() calls inside ROWS FROM(), and attach a column definition list to each one. 

...

select * from rows from (unnest(array[1,2]), unnest(array[3,4])) as (a int, b int); 

错误：

ROWS FROM() with multiple functions cannot have a column definition list 
LINE 1: ...from (unnest(array[1,2]), unnest(array[3,4])) as (a int, b i... 
                  ^
HINT: Put a separate column definition list for each function inside ROWS FROM(). 

该手册也解释了这一点如何定义这些'单独的列定义'？

Answer 1

您可以直接用AS t(a, b)没有定义它们的类型的列名：

#= SELECT * FROM unnest(array[1,2], array[3,4,5]) AS t(a, b); 
a | b 
---+--- 
1 | 3 
2 | 4 
∅ | 5 

要定义类型，这样做对这种阵列本身：

#= SELECT a/2 AS half_a, b/2 AS half_b 
    FROM unnest(array[1,2]::float[], array[3,4,5]::integer[]) AS t(a, b); 
half_a | half_b 
--------+-------- 
    0.5 |  1 
     1 |  2 
     ∅ |  2