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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
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SQL uses NULLs as a special flag that signals the lack of a value for a field or a variable. NULLs should be used wisely so the database gives a faithful picture of the reality it represents.
In SQL, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F.
No its not the same as null means a value that is unavailable unassigned or unknown and zero is a defined value. The intersection of any two disjoint sets is a null set. Justify your answer.
The notation COUNT(*) includes NULL values in the total. The notation COUNT( column_name ) only considers rows where the column contains a non- NULL value.
Aliasing can be used in a number of ways, not just to shorten a long column name.
In this case, your example means you're returning a column that always contains NULL, and it's alias/column name is aColumn.
Aliasing can also be used when you're using computed values, such as Column1 + Column2 AS Column3.
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When unioning or joining datasets using a 'Null AS [ColumnA] is a quick way to make sure create a complete dataset that can then be updated later and a new column does not need to be created in any of the source tables.
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