uCertify Articles » OCA DBA 11g http://www.ucertify.com/article Just another WordPress weblog Wed, 04 Nov 2009 00:00:00 +0000 http://wordpress.org/?v=2.8.4 en hourly 1 OCP 1z0-047 Short Notes: Exam passing tips http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html#comments Sat, 03 Oct 2009 00:00:00 +0000 uCertify 3701677

Retrieving data using the SQL SELECT statement and using single row functions to customize the output

  • /*…*/ and — are used to put comments in an Oracle program.

  • The CREATE TABLE does not end immediately with a semicolon, and a column name cannot start with a numeric value. However, a numeric value can be used in between a column name.

  • Name of a table cannot start with @ special character.

  • Knowing about the GROUP BY clause.

Using sub queries and set operators to solve queries, as well as DDL statements to create and manage tables

  • + (unary), – (unary), *, /, ||, =, !=, <, >, <=, >=, IS NULL, LIKE, BETWEEN, IN, NOT, AND, OR is the correct order of operators precedence.

  • The ROLLBACK command is used to end the current transaction, and discard any changes made since the beginning of the transaction.

Managing objects with data dictionary views, schema objects and data in different time zones

  • The length of a column can be increased even if it contains data. However, the data type of the column cannot be modified if it contains any data.

  • The parameters used to maximize the space in Flash Recovery Area.

  • User error failure refers to a database failure that results due to certain transactions on a database by a user.

  • Flashback Query is used to view and repair historical data, and to view the contents of a table at any specific point in time.

  • UNDO_RETENTION is a parameter in the init.ora initialization parameters file that specifies the time period in seconds for which a system retains undo data for committed transactions.

  • Once the Flashback Versions Query is run to diagnose the erroneous transaction, the Flashback Transaction Query helps in the repair process of the transaction.

  • The correct order of steps that will enable the flashback database are as follows:
    1. Put the database in Archive log mode.
    2. Set up a flash recovery area.
    3. Set the period for the flashback retention target.
    4. Shut down and mount the database.
    5. Enable flashback logging.
    6. Open the database.
  • The overall utilization of the flash recovery area is displayed in megabytes.

  • SQL statement can be used to flashback a database.

  • Take the following steps to enable the Flashback Database:
    1. Ensure that the database is in Archive Log mode.

    2. Setup a flash recovery area.

    3. Set the duration for the flashback retention target.

    4. Shutdown the database.

    5. Mount the database.

    6. Enable flashback logging.

    7. Open the database.
  • The dropped table can be recovered by using Flashback Drop.

  • The flashback database is enabled only in Archive log mode, as it recovers the database to an earlier specific point of time.

  • Flashback Database is used to reverse the changes made to a table.

  • The Perform Recovery: Review screen is used to display the RMAN script that performs the Flashback Database recovery.

  • The portlist.ini file is used to get all the port numbers of the HTTP listeners.

  • RVWR is a background process, which is a part of the Flashback Database Architecture.

  • LGWR is a background process that is a part of Flashback Database Architecture.

  • SELECT oldest_flashback_scn FROM V; is used to retrieve an approximate system change number (SCN) to which a database can be flashed back.
Share/Bookmark]]> http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips-2.html/feed 0 What is the REMOTE_OS_AUTHENT parameter? http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html#comments Wed, 30 Sep 2009 00:00:00 +0000 uCertify 3701252

The REMOTE_OS_AUTHENT parameter in the parameter file of the database specifies whether remote clients will be authenticated with the value of the OS_AUTHENT_PREFIX parameter or not. The type of the REMOTE_OS_AUTHENT parameter is Boolean, the default value is false, and the parameter class is static. The REMOTE_OS_AUTHENT parameter is case sensitive on some operating systems. The flow diagram below may help a user understand the role of the REMOTE_OS_AUTHENT parameter for a remote database:

Share/Bookmark]]> http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter-2.html/feed 0 What is DBMS_SESSION PL/SQL package? http://www.ucertify.com/article/what-is-dbms_session-plsql-package-2.html http://www.ucertify.com/article/what-is-dbms_session-plsql-package-2.html#comments Tue, 08 Sep 2009 00:00:00 +0000 uCertify 2201023

The DBMS_SESSION PL/SQL package is used to provide access to the ALTER SESSION and ALTER SYSTEM statements. This package is also used for gathering session related information. The DBMS_SESSION PL/SQL package uses the privileges of the user executing this package, instead of using privileges of the user SYS.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-dbms_session-plsql-package-2.html/feed 0 What is DECODE function? http://www.ucertify.com/article/what-is-decode-function-2.html http://www.ucertify.com/article/what-is-decode-function-2.html#comments Tue, 01 Sep 2009 00:00:00 +0000 uCertify 1801007

The DECODE function decodes a column value or an expression and compares it with each specified search value, one by one. If the expression matches a search value, a result value corresponding to the matching search value is returned. If no match is found, a default result value, if included, is returned. However, if no default value is included, a NULL value is returned. The DECODE function is one of the few single-row functions that directly deal with NULL values. It can compare two NULL values and can return a NULL value.

Syntax:

DECODE (ColumnExpression, search, result[, search, result, ...] [, default] )

ColumnExpression, search, and result can be of the CHAR, VARCHAR2, NCHAR, or NVARCHAR2 datatype.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-decode-function-2.html/feed 0 What is TO_CHAR (datetime) function? http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html#comments Tue, 01 Sep 2009 00:00:00 +0000 uCertify 1801075

TO_CHAR (datetime) is a single-row function that is used to convert a value of DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, or TIMESTAMP WITH LOCAL TIME ZONE datatype to a value of VARCHAR2 datatype in the specified date format.

Syntax:

TO_CHAR ( datetime [, fmt [, 'nlsparam' ]] )

where,

  • datetime specifies a value of DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE, or TIMESTAMP WITH LOCAL TIME ZONE datatype.

  • fmt specifies the date format in which the converted value is to be displayed.

  • nlsparam specifies the language in which the names and abbreviations of months and days are to be displayed.
    • Share/Bookmark]]>     http://www.ucertify.com/article/what-is-to_char-datetime-function-2.html/feed 0     Joins: Its Types and Uses http://www.ucertify.com/article/joins-its-types-and-uses.html http://www.ucertify.com/article/joins-its-types-and-uses.html#comments Fri, 21 Aug 2009 00:00:00 +0000 uCertify 3601509

    The JOIN clause is used with the SELECT statement to retrieve data from more than one table. This clause matches data from multiple tables. This results in the creation of a table, which is a combination of columns from multiple tables.

    Uses of Joins: Join is a feature of SQL Server. It joins the tables by means of the combination of a primary key and a foreign key. The result of the query generates a temporary table containing the columns from two or more tables. An example of using the JOIN clause is as follows:

    Suppose there is a database named Manufacture, which contains the tables Car and Dealer. The Car table has the following columns:

    • CarID

    • CarName

    • CarModel

    • CarPrice

    The Dealer table has the following columns:

    • DealerID

    • DealerName

    • Address

    • Phone

    • Mobile

    • Commission
    • CarID

    The CarID column in the Car table is defined as the primary key, and the CarID column in the Dealer table is defined as the foreign key. If a user wants to retrieve the car name, car price, car model, dealer name, and commission, the following query should be executed:

    SELECT CarName, CarModel, CarPrice, DealerName, Commission FROM Car JOIN Dealer WHERE Car.CarID=Dealer.CarID

    Aliases: If two tables contain the same columns, it results in a conflict. To avoid this conflict, a user can use either the table names or aliases. The aliases improve the readability of a SQL statement. Aliases can be defined by using letters, numbers, or a combination of these. The following example will demonstrate the use of aliases:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c JOIN Dealer d WHERE Car.CarID=Dealer.CarID

    In the above example, c is the alias for the Car table, and d is the alias for the Dealer table.

    Types of Joins: The join types used in SQL Server are as follows:

    Inner Joins: In this type of join, data in various columns are compared by using the comparison operators. The inner joins are also known as equi-joins. It returns only those rows that have an equal value. The following example will demonstrate the use of the inner join:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c INNER JOIN Dealer d ON c.CarID=d.CarID

    Outer Joins: Outer joins return rows from one of the tables specified in the query. There are three types of outer joins as follows:

    LEFT OUTER JOIN: When this join is used in a query, all the rows from the left table will be retrieved, and only the matching rows from the right table will be retrieved. If a row from the left table does not match with any of the rows of the right table, NULL is inserted in that row of the right table. The following example will demonstrate the use of the LEFT OUTER JOIN:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c LEFT OUTER JOIN Dealer d ON c.CarID=d.CarID

    In the above example, all rows from the Car table will be retrieved, and only the matching rows from the Dealer table will be retrieved.

    RIGHT OUTER JOIN: When this join is used in a query, all the rows from the right table will be retrieved, and only the matching rows from the left table will be retrieved. If a row from the right table does not match with any of the rows of the left table, NULL is inserted in that row of the left table. The following example will demonstrate the use of the RIGHT OUTER JOIN:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c RIGHT OUTER JOIN Dealer d ON c.CarID=d.CarID

    In the above example, all rows from the Dealer table will be retrieved, and only the matching rows from the Car table will be retrieved.

    FULL OUTER JOIN: When this join is used in a query, all the rows from all the tables specified in the query will be retrieved. The following example will demonstrate the use of the FULL OUTER JOIN:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c FULL OUTER JOIN Dealer d ON c.CarID=d.CarID

    In the above example, all rows from the Dealer and Car tables will be retrieved.

    Cross Joins: When this join is used in a query, the result is the multiplication of the number of rows from the left table with the number of rows from the right table. The following example will demonstrate this:

    SELECT c.CarName, c.CarModel, c.CarPrice, d.DealerName, d.Commission FROM Car c CROSS JOIN Dealer d ON c.CarID=d.CarID

    If the Car table contains ten rows and the Dealer table contains twelve rows, the result will be 120 rows.

    Self Join: This join is used to join a table with itself. In this case, a user will have to use two unique aliases for the table. The following example will demonstrate this:

    SELECT c1.CarName, c1.CarModel, c1.CarPrice FROM Car c1 INNER JOIN Car c2 ON c1.CarID=c2.CarID

    Share/Bookmark]]>     http://www.ucertify.com/article/joins-its-types-and-uses.html/feed 0     Relational Algebra http://www.ucertify.com/article/relational-algebra.html http://www.ucertify.com/article/relational-algebra.html#comments Sat, 15 Aug 2009 00:00:00 +0000 uCertify 3501099

    Algebra is a formal structure, which consists of sets, and operations performed on these sets. Relational algebra is a formal structure for manipulating relations. There are various relational operators for manipulating relations. These operators take two tables, perform the operation, and return back the desired output.

    There are basically eight operators in relational algebra to perform operations on tables. Each of them is discussed in detail.

    1. Union
    2. Intersection
    3. Difference
    4. Cartesian Product
    5. Project
    6. Restrict
    7. Divide
    8. Join

    The first four operators, i.e. Union, Intersection, Difference, and Cartesian Product are taken from set theory with some changes to make them work with tables. The last four, i.e. Project, Restrict, Divide, and Join are designed specifically for tables. The most important operators for logical design are project and join.

    Union

    The union operator takes two tables and returns a table including all the rows appearing in either or both of the tables.

    Union is always denoted by the ‘U’ symbol. Suppose there is a table named P and a table named Q, then the union of the two will be PUQ.

    An example, which describes the union operation, is given below.

    P
    Name
    Roger
    John
    Jones
    		Q
    EmpId
    A11
    A12
    A13

    Result of P Union Q

    Name EmpId
    Roger A11
    John A12
    Jones A13

    Intersection

    The intersection operator takes two tables and returns a table, which consists of all the common rows appearing in both the tables. If no row is common between the two tables, then the result is NULL.

    Below is an example, which describes the intersection operation.

    P
    Name EmpId
    Roger A11
    Binnie A12
    Annie A13
    		Q
    Name EmpId
    Roger A11

    Result of P Intersection Q

    Name EmpId
    Roger A11

    Here, only one row is common between P and Q.

    Difference

    The difference operator takes two tables and returns a table, which consists of all rows appearing in one of the tables but not in the other. The symbol for difference is ‘-’. If there are two tables named A and B, then the difference between them is “A-B”. It consists of all the rows in A but not in B.

    Below is an example, which describes the difference operation.

    A
    Name
    Roger
    Annie
    Binnie
    Richie
    		B
    Name
    Anil
    Emma
    Rocky

    Result of A Difference B

    Name
    Roger
    Annie
    Binnie
    Richie

    Cartesian Product

    The Cartesian product operator takes two tables and returns a table that consists of rows that are possible combination of two rows, i.e. one from each table. The symbol of the Cartesian operator is ‘X’.

    Below is an example, which describes the Cartesian product.

    A
    Name
    Roger
    Binnie
    		B
    Working days
    Monday
    Tuesday
    Wednesday

    Resultant Table

    Name Working days
    Roger Monday
    Binnie Monday
    Roger Tuesday
    Binnie Tuesday
    Roger Wednesday
    Binnie Wednesday

    Here, the resultant table obtained is the possible combination of rows from both the tables.

    Project

    The project operator takes a table and returns a table that is a subset of the original table. The result obtained is known as projection. A projection is also known as decomposition of the table.

    To understand projection, let’s take an example. A table named Employee is given below. The projection of the table on two attributes, Empname and salary, is also shown below. The projection is the subset of the original table.

    Employee

    Name Salary DeptId
    Smith 800 30
    Harry 1250 30
    Warden 1260 30
    Blake 1245 30

    Result of Projection on the Employee table

    Name Salary
    Smith 800
    Harry 1250
    Warden 1260
    Blake 1245

    Restrict

    The restrict operator takes a table and returns a table that consists of a subset of rows. The selected rows must satisfy a specific criteria or restriction condition. It is implemented using the WHERE clause of the SELECT statement.

    The result so obtained is known as selection.

    An example, which describes the restrict operation, is given below.

    The table named student is given below:

    Name Age
    Lucky 12
    Linda 13
    Melinda 13
    Binnie 13
    James 12

    Now, when the following query is issued on this table, the result will be as follows:

    SELECT Name
    FROM Student
    WHERE age>12

    Linda
    Melinda
    Binnie

    Divide

    The divide operator takes two tables, one table having two columns and the other having one column. It searches in the two-column table for those sets of rows, for which the values in one of the two columns match all the values in the one-column table and for which all the corresponding row values in the second column are the same. The result obtained is a single-column table that consists of all the matching values found in the second column.

    An example, which describes the division operation, is given below.

    A table named student is given with two columns: Name and Grade; and a table named Grade is given with one column Grade.

    Name
    Name Grade
    Roger A
    Roger B
    Melinda A
    Melinda C
    Peter A
    Peter B
    Doreen B
    Doreen C
    		Grade
    Grade
    A
    B

    Resultant table

    Roger
    Peter

    The result contains the value from the Name table. The two names obtained have both the values that are in the Grade table. Only Roger and Peter contain matching values, i.e. A and B from the Grade table.

    Join

    A join or an equijoin combines the rows of two tables that have equivalent values for the specified columns. The two tables are joined using an equality operator “=”. It is also known as simple join and inner join. A join is basically a combination of Cartesian product and restrict operation. The join operation takes all the possible combination of rows from the two tables as it is done in Cartesian product, and then it selects those records for which the values in a common attribute meet some specified criteria. For example, consider the two tables given below named Employee and Salary. Here, the common attribute between the two tables is EmpId. When we perform a join on these two tables, then all the records, which have the same values on EmpId in both the tables will be retrieved. Hence, it is a combination of both Cartesian product and join operations.

    Employee
    Name EmpId
    Richard A11
    Doreen A12
    Peter A13
    Nancy A14
    		Salary
    EmpId Salary
    A11 2300
    A13 3000

    When we perform a join operation on these two tables, we get a result as given below:

    SELECT *
    FROM Employee, Salary
    WHERE Employee.EmpId= Salary.EmpId

    Result
    EmpId Name Salary
    A11 Richard 2300
    A13 Peter 3000

    The join and project operators are very important to normal forms. These operators specify whether a particular decomposition of table improves the logical design of the database or not.

    Note: Why is a relational database said to be “closed” when relational operators are applied to any of its tables?

    When a relational operator is applied to a table in a relational database, the result is another table. That means applying relational operators to the results of relational operations will yield another table. Therefore, a relational database is said to be closed when relational operators are applied to any of its tables.

    Share/Bookmark]]>     http://www.ucertify.com/article/relational-algebra.html/feed 0     OCP 1z0-047 Short Notes: Exam passing tips http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips.html http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips.html#comments Fri, 07 Aug 2009 00:00:00 +0000 uCertify 3701677

    Retrieving data using the SQL SELECT statement and using single row functions to customize the output

    • /*…*/ and — are used to put comments in an Oracle program.

    • The CREATE TABLE does not end immediately with a semicolon, and a column name cannot start with a numeric value. However, a numeric value can be used in between a column name.

    • Name of a table cannot start with @ special character.

    • Knowing about the GROUP BY clause.

    Using sub queries and set operators to solve queries, as well as DDL statements to create and manage tables

    • + (unary), – (unary), *, /, ||, =, !=, <, >, <=, >=, IS NULL, LIKE, BETWEEN, IN, NOT, AND, OR is the correct order of operators precedence.

    • The ROLLBACK command is used to end the current transaction, and discard any changes made since the beginning of the transaction.

    Managing objects with data dictionary views, schema objects and data in different time zones

    • The length of a column can be increased even if it contains data. However, the data type of the column cannot be modified if it contains any data.

    • The parameters used to maximize the space in Flash Recovery Area.

    • User error failure refers to a database failure that results due to certain transactions on a database by a user.

    • Flashback Query is used to view and repair historical data, and to view the contents of a table at any specific point in time.

    • UNDO_RETENTION is a parameter in the init.ora initialization parameters file that specifies the time period in seconds for which a system retains undo data for committed transactions.

    • Once the Flashback Versions Query is run to diagnose the erroneous transaction, the Flashback Transaction Query helps in the repair process of the transaction.

    • The correct order of steps that will enable the flashback database are as follows:
      1. Put the database in Archive log mode.
      2. Set up a flash recovery area.
      3. Set the period for the flashback retention target.
      4. Shut down and mount the database.
      5. Enable flashback logging.
      6. Open the database.
    • The overall utilization of the flash recovery area is displayed in megabytes.

    • SQL statement can be used to flashback a database.

    • Take the following steps to enable the Flashback Database:
      1. Ensure that the database is in Archive Log mode.

      2. Setup a flash recovery area.

      3. Set the duration for the flashback retention target.

      4. Shutdown the database.

      5. Mount the database.

      6. Enable flashback logging.

      7. Open the database.
    • The dropped table can be recovered by using Flashback Drop.

    • The flashback database is enabled only in Archive log mode, as it recovers the database to an earlier specific point of time.

    • Flashback Database is used to reverse the changes made to a table.

    • The Perform Recovery: Review screen is used to display the RMAN script that performs the Flashback Database recovery.

    • The portlist.ini file is used to get all the port numbers of the HTTP listeners.

    • RVWR is a background process, which is a part of the Flashback Database Architecture.

    • LGWR is a background process that is a part of Flashback Database Architecture.

    • SELECT oldest_flashback_scn FROM V; is used to retrieve an approximate system change number (SCN) to which a database can be flashed back.
    Share/Bookmark]]>     http://www.ucertify.com/article/ocp-1z0-047-short-notes-exam-passing-tips.html/feed 0     What is the REMOTE_OS_AUTHENT parameter? http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter.html http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter.html#comments Tue, 04 Aug 2009 00:00:00 +0000 uCertify 3701252

    The REMOTE_OS_AUTHENT parameter in the parameter file of the database specifies whether remote clients will be authenticated with the value of the OS_AUTHENT_PREFIX parameter or not. The type of the REMOTE_OS_AUTHENT parameter is Boolean, the default value is false, and the parameter class is static. The REMOTE_OS_AUTHENT parameter is case sensitive on some operating systems. The flow diagram below may help a user understand the role of the REMOTE_OS_AUTHENT parameter for a remote database:

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-the-remote_os_authent-parameter.html/feed 0     What are conventional path loads? http://www.ucertify.com/article/what-are-conventional-path-loads.html http://www.ucertify.com/article/what-are-conventional-path-loads.html#comments Mon, 27 Jul 2009 00:00:00 +0000 uCertify 2201079

    A conventional path load is a method of loading data into tables. This method uses the SQL INSERT statement and a bind array buffer for loading the data. It is the default method employed by every Oracle tool and application. In conventional path loads, the SQL*Loader has to compete with all other Oracle processes for buffer resources. However, this significantly deteriorates the speed of the load process as compared to direct path loads. Conventional path loads search for partially filled data blocks to fill them at each insert operation. This process also deteriorates the speed of conventional path loads. Conventional path loads are generally employed for loading data into clustered tables or where a small number of rows are to be inserted into a large indexed table.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-are-conventional-path-loads.html/feed 0