Database and SQL

This type of lock in Oracle locks the table allowing other user to only query but not insert, update or delete rows in table.

This component of select statement tells the database how a user wants the data to be summarised.

This constraint in Oracle allows an entity to represent a table and each row of the table represents an instance of that entity.

This is true choice. Q statement is correct because the primary key and the foreign key can exist in the same relation. Moreover foreign key can refer to the primary key in the same relation.So, this is a correct choice.

Option P is correct because a candidate key is a key that uniquely identifies a row in a relation. So, this cannot be null as it uniquely identifies a row. Option R is correct because primary key is chosen from a set of candidate keys. In other words all the candidate keys are the candidates for the primary key. So, in this way all the candidate keys are primary keys. So, this is the correct answer.

Alter table command is used in SQL to alter the definition of already existing table.

Drop is used to delete table/view/synonym in SQL.

A default value can be specified for a column using the default clause.

This function returns sign of a given number.

This function is used to convert a given string to equivalent number in SQL.

This type of entity constraint in DBMS requires that an entity belongs to no more than one lower level entity set.

In a database relation, when one or more fields serve as primary key, then such a key is called composite key.

This object in SQL is a predicate expressing a condition that we wish the database always to satisfy.

This normal form in DBMS states that every determinant in the database is a candidate key.

This is the first step in executing a SQL query in DBMS as once a query is entered into the system its meaning is to be clearly understood by the compiler.