Which of the following is a legal expression in SQL?

Among all the options given, the option that is true for Which of the following is a legal expression in SQL? is

 option 1 which refers to the “ case expression”. The case expression is used for conditional logic within a query. Here is the example given:-

SELECT 
    CASE 
        WHEN age >= 18 THEN ‘Adult’ 
        ELSE ‘Minor’ 
    END AS AgeCategory 
FROM Users;

Option 2 which refers to the “ order by the expression” is not considered a legal expression. You would need to repeat the expression or you can use the positional reference of your columns.

Option 3 which refers to the “ Where clause expression” is also not considered a legal expression in SQL. SQL doesn’t allow an alias defined in the “SELECT” clause directly in the “WHERE” clause.

Option 4 which refers to the “ Group by the expression” is again not a fact regarding legal expression in SQL.

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