Quick Info (IntelliSense)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
The Microsoft IntelliSense Quick Info option displays the complete declaration for any identifier in your code. When you move the mouse pointer over an identifier, its declaration is displayed in a yellow pop-up window. In SQL Server Management Studio, Quick Info is available in the Database Engine and XML Query Editors.
Transact-SQL Quick Info
Quick Info displays two types of information in the Database Engine Query Editor. When not in debug mode, Quick Info displays the expression declaration. When in debug mode, Quick Info instead displays the name of the expression and its current value.
In the Database Engine Query Editor, Quick Info is available only for those parts of the Transact-SQL syntax that IntelliSense supports. For example, if you move the mouse pointer over the identifier for an object that has a data type that IntelliSense does not support, the Quick Info pop-up window contains a message that states that the data type is not supported.