从 do 块返回查询

我想做的就是能够使用do块设置一些变量，然后返回一个查询STDOUT使用这些变量。

DO $$
DECLARE book_name TEXT;
DECLARE book_slug TEXT;
BEGIN
  book_name := 'Ise Monogatari';
  book_slug := 'ise';

  SELECT bk.id,
    bk.created_at,
    bk.updated_at,
    bk.title,
    bk.japanese_title,
    bk.content,
    bk.description,
    'public/cjp/' || book_slug || '/images/cover.png' cover_image_path,
    'public/cjp/' || book_slug || '/images/title.png' title_image_path,
    'public/cjp/' || book_slug || '/images/thumb_left.png' thumbnail_path,
    'public/cjp/' || book_slug || '/images/background.png' background_image_path,
    bk.about,
    bk.published
  FROM books bk
  WHERE bk.title = book_name;
END $$;

我收到以下错误：

[42601] ERROR: query has no destination for result data
Hint: If you want to discard the results of a SELECT, use PERFORM instead.
Where: PL/pgSQL function inline_code_block line 8 at SQL statement

任何帮助表示赞赏。

您无法从 DO 命令返回任何结果。文档说 https://www.postgresql.org/docs/current/static/sql-do.html（强调）：

代码块被视为没有参数的函数体，返回无效。

您可以使用公用表表达式：

WITH args(book_name, book_slug) AS (
    VALUES ('Ise Monogatari', 'ise')
)

  SELECT bk.id,
    bk.created_at,
    bk.updated_at,
    bk.title,
    bk.japanese_title,
    bk.content,
    bk.description,
    'public/cjp/' || book_slug || '/images/cover.png' cover_image_path,
    'public/cjp/' || book_slug || '/images/title.png' title_image_path,
    'public/cjp/' || book_slug || '/images/thumb_left.png' thumbnail_path,
    'public/cjp/' || book_slug || '/images/background.png' background_image_path,
    bk.about,
    bk.published
  FROM books bk
  CROSS JOIN args
  WHERE bk.title = book_name;