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UNIT P UNIT_CODE CHAR (8) UNIT NAME VARCHAR (50) ++ + ENROLMENT OPF STU_NBR NUMERIC (8) PF UNIT CODE CHAR (8) P" ENROL YEAR NUMERIC (4) PENROL SEMESTER CHAR (2) ENROL MARK NUMERIC 3 ENROL GRADE CHAR (2) STUDENT STU_NBR NUMERIC (8) STU LNAME VARCHAR (50) STU FNAME VARCHAR (50) STU_DOB Date If we are going to create a database based on the above diagram, how many primary key constraints do we need to create? Select one: a. 6 O b. 4 O c. 2 O d. 3 When writing SQL table-creating command sequences, the entire table definition is enclosed in Select one: O a. parentheses b. commas C. asterisks d. quotations Words used by a system that cannot be used for any other purpose are called words. For example, in Oracle SQL, the word INITIAL cannot be used to name tables or columns. Select one: O a. null b. reserved O c. character d. unique The constraint is used to validate data when an attribute value is entered. Select one: O a. UNIQUE O b. CHECK C. CASCADE O d. SET NULL