Differences between Select and SET on variable assignments in SQL Server stored procedures

There are two ways to assign values to variables that are already defined in SQL Server, SET and SELECT, respectively.
The differences between these two approaches are explained in more detail in SQL Server Books Online, but many times we
Did not notice, in fact, these two ways still have a lot of differences.

SQL Server recommends using SET instead of SELECT to assign a value to a variable.
The SET method is recommended when an expression returns a value and assigns a variable to it.

The following table lists the differences between SET and SELECT. Please pay special attention to the red section.

	Set	Select
Simultaneously assign values to multiple variables simultaneously	Not supported	Support
When an expression returns multiple values	Error	Assigns the last value returned to the variable
Expression does not return a value	variable is assigned a null value	The variable holds the original value

Differences between Select and SET on variable assignments in SQL Server stored procedures