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The CUSTOMERS table has these columns: 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   WHERE 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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