单选题Which statement adds a constraint that ensures the CUSTOMER_NAME column of the CUSTOMERS table holds a value?（）AALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;BALTER TABLE customers MODIFY CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;CALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn NOT NULL;DALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn IS NOT NULL;EALTER TABLE customers MODIFY name CONSTRAINT cust_name_nn NOT NULL;FALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name NOT NULL;
单选题
Which statement adds a constraint that ensures the CUSTOMER_NAME column of the CUSTOMERS table holds a value?（）
A
ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;
B
ALTER TABLE customers MODIFY CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;
C
ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn NOT NULL;
D
ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn IS NOT NULL;
E
ALTER TABLE customers MODIFY name CONSTRAINT cust_name_nn NOT NULL;
F
ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name NOT NULL;
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