View the Exhibit and examine the description for the CUSTOMERS table.
You want to update the CUST_CREDIT_LIMIT column to NULL for all the customers, where CUST_INCOME_LEVEL has NULL in the CUSTOMERS table.
Which SQL statement will accomplish the task?
A.
UPDATE customers
SET cust_credit_limit = NULL
WHERE CUST_INCOME_LEVEL = NULL;
B.
UPDATE customers
SET cust_credit_limit = NULL
WHERE cust_income_level IS NULL;
C.
UPDATE customers
SET cust_credit_limit = TO_NUMBER(NULL)
WHERE cust_income_level = TO_NUMBER(NULL);
D.
UPDATE customers
SET cust_credit_limit = TO_NUMBER(‘ ‘,9999)
WHERE cust_income_level IS NULL;
Is
= NULL (equal NULL)
the same as
IS NULL?
besides that one “makes sense” and the other will never return any rows?
nothing is equal to null
nothing is NOT equal to null
but a NULL can be “null”. When you need to retrieve NULLS, you must use “is null”
ops$tkyte@ORA9IR2> select * from dual where null=null;
no rows selected
ops$tkyte@ORA9IR2> select * from dual where null null;
no rows selected
ops$tkyte@ORA9IR2> select * from dual where null IS null;
D
–
X
(ask.Tom)
Why is D wrong?
there is space in to_number(‘ ‘,9999) thats why it is wrong
Because this space is considered a character, and the question is to update to NULL. Sorry if my english is not good.
Because this space is considered a character, and the question is to update to NULL. Sorry if my english is not good.
B is correct
B.
UPDATE customers
SET cust_credit_limit = NULL
WHERE cust_income_level IS NULL;