I don't get this. Are there any documentation that helps explain this further?
I don't understand the difference between string literals and column aliases, and why those two has to be identified using different type of quotes? Are there other cases where different quotes has to be used?
Steven Parker170,333 Points
For the most part, you will use single quotes with SQL. Double quotes are rarely needed, and generally only when a column name (either an actual column or an alias) contains some unusual character like a space or symbol. The key to remember is single is for string, and double is for identifier.
The SQLite database used in the courses is more flexible that most, as it will allow the use of single or double quotes for both identifiers and strings. But it's good to get in the habit of using them in the "official" way so you can work with other databases easily later.
So in simple terms - if you need to concatenate a string with a column then use single quotes - if you are alias a column then use double quote marks.