使用缩进查询输出 [英] Query output with indentation

问题描述

我有表System

component | subcomponent  (foreign key with subsystem table)
----------+-------------
cpu       |  1
monitor   |
lcd       |
keybord   |
mouse     |

子组件表

id  | name
----+-------------
1   | motherboard
1   | harddisk
1   | cdrom

现在我要打印带有缩进

所需的输出

cpu
   --motherboar
   --harddisk
   --cdrom
keyboard
mouse
lcd

怎么可能？

推荐答案

可以使用例如左联接和一些字符串格式设置功能：

It's possible using e.g. a left join and some of the string formatting functions:

select ... as parent, '  -- ' || coalesce(..., '') as child
from ... left join ... on ...

您也可以合并东西，等等，以获取所需的内容。

You could also union things instead, etc. to get exactly what you requested.

但正如已经建议的那样，将其保留在视图之外。

BUT you really ought to leave that up to the view, as already suggested.

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