Which of the following SQL statement(s) return an error (s)?SELECT NULL FROM Customer;SELECT NAME FROM Customer WHERE SALARY = NULL;SELECT NAME FROM Customer;SELECT ALL FROM Customer WHERE SALARY = NULL;SELECT NAME,NIC FROM Customer;
Question
Which of the following SQL statement(s) return an error (s)?SELECT NULL FROM Customer;SELECT NAME FROM Customer WHERE SALARY = NULL;SELECT NAME FROM Customer;SELECT ALL FROM Customer WHERE SALARY = NULL;SELECT NAME,NIC FROM Customer;
Solution
The following SQL statements will return an error:
-
SELECT NULL FROM Customer;- This statement will return an error because NULL is not a column name or a valid SQL command. -
SELECT NAME FROM Customer WHERE SALARY = NULL;- This statement will not return an error, but it will not return any results either. In SQL, NULL is not comparable, so you cannot use the equals (=) operator with NULL. Instead, you should use the IS NULL or IS NOT NULL operators. -
SELECT ALL FROM Customer WHERE SALARY = NULL;- This statement will return an error because ALL is not a valid SQL command. If you want to select all columns from the Customer table, you should use the asterisk (*) symbol, like this: SELECT * FROM Customer. Also, as mentioned above, you cannot use the equals (=) operator with NULL.
So, the correct versions of these statements would be:
-
SELECT * FROM Customer;- This will select all columns from the Customer table. -
SELECT NAME FROM Customer WHERE SALARY IS NULL;- This will select the NAME column from the Customer table for all rows where the SALARY is NULL. -
SELECT * FROM Customer WHERE SALARY IS NULL;- This will select all columns from the Customer table for all rows where the SALARY is NULL.
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