TAILIEUCHUNG - OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P35

OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P35:There is an ever increasing demand for staff with IT industry certification. The benefits to employers are significant—they can be certain that staff have a certain level of competence—and the benefits to the individuals, in terms of demand for their services, are equally great. Many employers are now requiring technical staff to have certifications, and many IT purchasers will not buy from firms that do not have certified staff. | OCA OCP Oracle Database 11g All-in-One Exam Guide 296 any user irrespective of which schema owns the views and tables or even in which database the tables reside. Consider this statement select from The user issuing the statement must know that the employees table is owned by the HR schema in the database identified by the database link PROD do not worry about database links they are a means of accessing objects in a database other than that onto which you are logged . If a public synonym has been created with this statement create public synonym emp for then all the user any user need enter is the following select from emp This gives both data independence and location transparency. Tables and views can be renamed or relocated without ever having to change code only the synonyms need to be adjusted. As well as SELECT statements DML statements can address synonyms as though they were the object to which they refer. Private synonyms are schema objects. Either they must be in your own schema or they must be qualified with the schema name. Public synonyms exist independently of a schema. A public synonym can be referred to by any user to whom permission has been granted to see it without the need to qualify it with a schema name. Private synonyms must have unique names within their schema. Public synonyms can have the same name as schema objects. When executing statements that address objects without a schema qualifier Oracle will first look for the object in the local schema and only if it cannot be found will it look for a public synonym. Thus in the preceding example if the user happened to own a table called EMP it would be this that would be seen not the table pointed to by the public synonym. The syntax to create a synonym is as follows CREATE PUBLIC SYNONYM synonym FOR object A user will need to have been granted permission to create private synonyms and further permission to create public synonyms. Usually only the database

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