如何使用MySQL SELECT创建虚拟列? [英] How to create virtual column using MySQL SELECT?

问题描述

如果我选择了一个AS b并且b不是表中的一列，查询会创建虚拟"列吗?

If I do SELECT a AS b and b is not a column in the table, would query create the "virtual" column?

实际上，我需要在查询中合并一些虚拟列，并在查询中处理一些信息，以便以后可以在每个项目中使用它.

in fact, I need to incorporate some virtual column into the query and process some information into the query so I can use it with each item later on.

推荐答案

类似的东西

SELECT id, email, IF(active = 1, 'enabled', 'disabled') AS account_status FROM users

这使您可以进行操作并将其显示为列.

This allows you to make operations and show it as columns.

您还可以使用联接并将操作显示为列:

you can also use joins and show operations as columns:

SELECT u.id, e.email, IF(c.id IS NULL, 'no selected', c.name) AS country
FROM users u LEFT JOIN countries c ON u.country_id = c.id

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