This is a post in the SQL Interview series. These aren't trick or gotcha questions, they're just questions designed to scope out a candidate's knowledge around SQL Server and Azure SQL Database.
Many versions of SQL require every SQL statement to be terminated with a semicolon.
Since it was created, T-SQL has listed statement terminators as optional.
Are there any situations where they are required, and not optional?
Since SQL Server 2005, some T-SQL statements must be separated from previous statements by a statement terminator.
The statements involved are WITH, SEND, RECEIVE.
In addition, a MERGE statement must have a statement terminator.
Using statement terminators is generally considered good practice, even though many of the Microsoft-supplied tools generate scripts without them.
Ever since SQL Server 2005, the product deprecation list has stated that the optional nature of statement terminators is deprecated. For this reason alone, you should use statement terminators.
But there are other potential issues. Consider this nasty example from fellow MVP Erland Sommarskog:
SELECT 1/0 AS CauseAnException
What is not immediately obvious is that THROW would never be executed. Instead, it would be interpreted as a column alias for ERROR_MESSAGE().
Using semicolons as statement terminators avoids this type of issue.