从字符串数组创建一个 table

Question

基本上，当给定一个字符串列表时，

我想用 select 语句创建一个 table。

例如，

"A", "B", "C",

我想创建一个 table 作为子 select，例如：

sub-select
+---------+
|   "A"   |
+---------+
|   "B"   |
+---------+
|   "C"   |
+---------+

如何在 redshift 和 postgres 中执行此操作？

谢谢！

更新：

select 'a' as A;

是我想要的 returns:

     a
+---------+
|   "a"   |
+---------+

如何从查询 select 'a' as A;

中为该列 a 设置多行

Answer 1

没有机会在数据库中测试它，但类似的东西

select * INTO table from (
SELECT CAST('A' AS VARCHAR(100)) AS col
UNION ALL
SELECT 'B' AS col
UNION ALL
SELECT 'C' AS col
) a

Answer 2

您可以使用 string_to_array 和 unnest

select *
from unnest(string_to_array('"A","B","C"', ','))

（但我不知道在 Redshift 中是否可用）

Answer 3

将列值转换为多行的方法之一是使用 split_part 函数和 UNION。

这是一个例子。

来源Table:

=> CREATE TABLE t_csv (value varchar(64));
=> INSERT INTO t_csv VALUES ('"A","B","C"');
=> INSERT INTO t_csv VALUES ('"D","E"');
=> INSERT INTO t_csv VALUES ('"F","G","H","I"');
=> SELECT * FROM t_csv;
      value
-----------------
 "D","E"
 "A","B","C"
 "F","G","H","I"
(3 rows)

这是获取多行的查询。

=> WITH a AS (SELECT value FROM t_csv)
SELECT * FROM
(
SELECT split_part(a.value,',',1) AS value FROM a
UNION
SELECT split_part(a.value,',',2) AS value FROM a
UNION
SELECT split_part(a.value,',',3) AS value FROM a
UNION
SELECT split_part(a.value,',',4) AS value FROM a
)
WHERE value != '';
value
-------
 "A"
 "B"
 "C"
 "D"
 "E"
 "F"
 "G"
 "H"
 "I"
(9 rows)

从字符串数组创建一个 table

From a string array, create a table

sql

postgresql

amazon-redshift