Which of the following must be enclosed in double quotes?

Solution(By Examveda Team)

In SQL, all of the above options must be enclosed in double quotes under specific circumstances.

Dates: When using a date literal in SQL, it should be enclosed in single quotes, like '2023-10-20'. Double quotes are typically not used for dates.
Column Alias: If you want to give a column an alias (a name that represents the column in the result set), you can enclose the alias in double quotes if it contains spaces or special characters. For example, if you want to alias a column as "Total Sales," you would write it as "Total Sales". However, it's not necessary to use double quotes for aliases without spaces or special characters.
Strings: When working with string values that contain spaces, special characters, or reserved keywords, you should enclose the string in single quotes (e.g., 'John Doe'). Double quotes are sometimes used to enclose identifiers (like table or column names) but not for string values.
So, the correct answer is Option D, as all of the mentioned elements may need double quotes, but it depends on the specific context and requirements in SQL.