SQL:NULL作为ColumnName意味着什么 [英] SQL: What does NULL as ColumnName imply

问题描述

我知道AS用于创建别名.因此，将一个长名称别名为一个短名称是有意义的.但是，我看到一个SQL查询NULL as ColumnName 这意味着什么?

I understand that AS is used to create an alias. Therefore, it makes sense to have one long name aliased as a shorter one. However, I am seeing a SQL query NULL as ColumnName What does this imply?

SELECT *, NULL as aColumn

推荐答案

别名可以以多种方式使用，而不仅仅是缩短长列名称.

Aliasing can be used in a number of ways, not just to shorten a long column name.

在这种情况下，您的示例意味着您返回的列始终包含NULL，并且其别名/列名称为aColumn.

In this case, your example means you're returning a column that always contains NULL, and it's alias/column name is aColumn.

在使用计算值(例如Column1 + Column2 AS Column3)时也可以使用别名.

Aliasing can also be used when you're using computed values, such as Column1 + Column2 AS Column3.

这篇关于SQL:NULL作为ColumnName意味着什么的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！