True or False, please explain why. 1, SQL (Structured Query Language) is both DD

ID: 3575685 • Letter: T

Question

True or False, please explain why.

1, SQL (Structured Query Language) is both DDL (Data Definition Language) and DML (Data Manipulation Language).

2, View is not updatable.

3, For Character data type, value NULL is equivalent to empty string ‘’.

4, A table has only one primary key, but it can have more than one foreign keys.

5, In SQL, an asterisk (*) can be used to express “all columns”.

6, If a schema satisfies BCNF, then it also satisfies 3NF.

7, A secondary index can be either dense or sparse.

8, Given a hash function h and two search-key values, Ki and kj, if kikj, then h(ki)h(kj).

9, Lname, Fname, Salary(salary>30000(Employee)) is equivalent to salary>30000(Lname, Fname, Salary(Employee)).

10, since Natural-join operations are associative, (E1 E2) E3 = E1 (E2 E3), the ordering of natural-join is not important for query optimization.

1.True, SQL is both DML and DDL because DML used to manipulate which are created bt DDL.

2. True, because View is used to show up-to-date data not update.

3. True, in SQL the character data type value is null is equal to empty string.

4. True, for one table we have only one primary key because for unique identification.

5. True, * (asterisk) means all fields or columns.

6. True

8. False, Because collision occurs when h(ki) = h(kj) then Ki != Kj, minimum number of collisons depends on hash function.

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