TAILIEUCHUNG - OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P32

OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P32: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 266 The DATE data type always includes century year month day hour minute and second even if all these elements are not specified at insert time. Year month and day must be specified if the hours minutes and seconds are omitted they will default to midnight. Exercise 7-2 Investigate the Data Types in the HR Schema In this exercise find out what data types are used in the tables in the HR schema using two techniques. 1. Connect to the database as user HR with SQL Plus or SQL Developer. 2. Use the DESCRIBE command to show the data types in some tables describe employees describe departments 3. Use a query against a data dictionary view to show what columns make up the EMPLOYEES table as the DESCRIBE command would select column_name data_type nullable data_length data_precision data_scale from user_tab_columns where table_name EMPLOYEES The view USER_TAB_COLUMNS shows the detail of every column in every table in the current user s schema. Create a Simple Table Tables can be stored in the database in several ways. The simplest is the heap table. A heap table contains variable-length rows in random order. There may be some correlation between the order in which rows are entered and the order in which they are stored but this is not guaranteed and should not be relied upon. More advanced table structures such as the following may impose ordering and grouping on the rows or force a random distribution Index organized tables Store rows in the order of an index key. Index clusters Can denormalize tables in parent-child relationships so that related rows from different table are stored together. Hash clusters Force a random distribution of rows which will break down any ordering based on the entry sequence. Partitioned tables Store rows in separate physical structures the partitions allocating rows according to the value of a column. Using the more advanced table structures has no effect whatsoever on SQL. Every SQL statement

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