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The CUSTOMERS table has these columns: CUSTOMER_ID NUMBER(4) NOT NULL CUSTOMER_NAME VARCHAR2(100) NOT NULL STREET_ADDRESS VARCHAR2(150) CITY_ADDRESS VARCHAR2(50) STATE_ADDRESS VARCHAR2(50) PROVINCE_ADDRESS VARCHAR2(50) COUNTRY_ADDRESS VARCHAR2(50) POSTAL_CODE VARCHAR2(12) CUSTOMER_PHONE VARCHAR2(20) Which statement finds the rows in the CUSTOMERS table that do not have a postal code?（）
A:SELECT customer_id, customer_name FROM customers WHERE postal_code CONTAINS NULL;
B:SELECT customer_id, customer_name FROM customers WHER postal_code = ' ___________';
C:SELECT customer_id, customer_name FROM customers WHERE postal _ code IS NULL;
D:SELECT customer_id, customer_name FROM customers WHERE postal code IS NVL;
E:SELECT customer_id, customer_name FROM customers WHERE postal_code = NULL;

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出自：Oracle认证

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