引用行对象的字段

Question

我无法访问我在 Presto 中创建的行对象的字段。 Presto 文档 claims "fields... are accessed with field reference operator." 但是这似乎不起作用。此代码重现了问题：

CREATE TABLE IF NOT EXISTS data AS
SELECT * FROM (VALUES
    (1, 'Adam', 17),
    (2, 'Bill', 42)
) AS x (id, name, age);

CREATE TABLE IF NOT EXISTS ungrouped_data AS
 WITH grouped_data AS (
  SELECT
    id,
    ROW(name, age) AS name_age
  FROM data
 )
SELECT
  id,
  name_age.1 AS name,
  name_age.2 AS age
FROM grouped_data;

其中 returns 一个 "extraneous input '.1'" 错误。

Answer 1

ROW(name, age) 将创建一个没有字段名称的行。今天要访问此类行中的字段，您需要将其转换为带有字段名称的行。试试这个：

WITH grouped_data AS ( 
    SELECT 
      id, 
      CAST(ROW(name, age) AS ROW(col1 VARCHAR, col2 INTEGER)) AS name_age 
    FROM data 
) 
SELECT 
  id, 
  name_age.col1 AS name, 
  name_age.col2 AS age 
FROM grouped_data;

结果：

 id | name | age
----+------+-----
  1 | Adam |  17
  2 | Bill |  42

有关这方面的讨论，请参阅 https://github.com/prestodb/presto/issues/7640。

Answer 2

使用 [] 运算符从 Trino (formerly known as Presto) 314, it is now possible to reference ROW 字段开始。

WITH grouped_data AS (
  SELECT
    id,
    ROW(name, age) AS name_age
  FROM data
)
SELECT
  id,
  name_age[1] AS name,
  name_age[2] AS age
FROM grouped_data;

引用行对象的字段

Reference to a field of a row object

presto

trino