uCertify Articles » 1Z0-001 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 What is the structure of a PL/SQL block? http://www.ucertify.com/article/what-is-the-structure-of-a-plsql-block.html http://www.ucertify.com/article/what-is-the-structure-of-a-plsql-block.html#comments Wed, 22 Jul 2009 00:00:00 +0000 uCertify 1801277

Procedural Language/Structured Query Language (PL/SQL) is a procedural language extension to SQL, the standard data access language for relational databases. PL/SQL is not an Oracle product in its own right; rather, it is a technology used by Oracle server and certain Oracle tools.

PL/SQL offers modern software engineering features (such as data encapsulation, exception handling, object orientation, and information hiding) and brings hi-tech programming to the Oracle server and toolset. It also incorporates many of the advanced features of the third generation programming languages. It allows the SQL statements to be included in block-structured and procedural units of code. In this way, PL/SQL combines the ease and flexibility of SQL with the structured programming language constructs such as IF…THEN, WHILE, and LOOP, thereby making PL/SQL a powerful transaction processing language.

PL/SQL blocks are passed to and processed by a PL/SQL engine, which may reside within the Oracle tool that passes the blocks or within the Oracle server. The engine that is actually used depends on from where the PL/SQL block is being invoked. When PL/SQL blocks are submitted from a Pro*C or a Pro*Cobol program, iSQL*Plus, or Server Manager, then the PL/SQL engine in the Oracle server processes them. The PL/SQL engine separates the SQL statements and sends them individually to the SQL statements executer.

A PL/SQL program is comprised of one or more PL/SQL blocks. These blocks can be entirely separate or nested within one another. A PL/SQL block may consist of the following three sections:

  • Declarative: The declarative section of a PL/SQL block contains all variables, constants, cursors, and user-defined exceptions that are referenced in the executable and declarative sections. The declarative section is optional in a PL/SQL block.
  • Executable: The executable section contains SQL and PL/SQL statements to manipulate data in the database and in the block, respectively. The executable section is mandatory in a PL/SQL block.
  • Exceptional: The exceptional section specifies the actions to be performed when errors or abnormal conditions arise in the executable section. This section is optional.

Following is the structure of a PL/SQL block:

DECLARE     -Optional
   Variables, cursors, user-defined exceptions
BEGIN     -Mandatory
   SQL statements
   PL/SQL statements
EXCEPTION     -Optional
   Actions to be performed when errors occur
END;     -Mandatory

A semicolon (;) must be placed at the end of a SQL statement or PL/SQL control statement. Section keywords (DECLARE, BEGIN, and EXCEPTION) are not followed by semicolons. The END section keyword and all other PL/SQL statements require a semicolon to terminate the statement. The statements can be stringed together on the same line, but this method is not recommended for clarity and editing. When a PL/SQL block is executed successfully without unhandled errors or compile errors, a message reading ‘PL/SQL procedure successfully completed’ should be displayed.

Basically, there are two types of PL/SQL blocks: anonymous block and subprogram. The basic units (subprograms and anonymous blocks) that make up a PL/SQL program are logical blocks, which can contain any number of nested sub blocks. Therefore, one block can represent a small part of another block, which in turn can be a part of the whole unit of code.

Anonymous block: An anonymous block is an unnamed PL/SQL block. In an application, an anonymous block is declared at the point where it is to be executed and is passed to the PL/SQL engine for execution at run time. An anonymous block can be embedded within a precompiler program, iSQL*Plus, or Server Manager. Triggers in Oracle Developer components consist of such blocks.

Subprogram: A subprogram is a named PL/SQL block that can accept parameters and can be invoked. There are two types of subprograms: procedure and function. Subprograms can be stored at the server or application level. By using Oracle Developer components (Forms, Reports, and Graphics), procedures and functions can be declared as part of an application (a form or report) and be called from other procedures, functions, and triggers within the same application whenever necessary.

  • Procedure: A procedure is a named PL/SQL block that can accept parameters (sometimes referred to as arguments) and be invoked. Generally, a procedure is used to perform an action. A procedure has a header, a declaration section, an executable section, and an optional exception-handling section. A procedure may or may not return values to its calling environment.

    A procedure can be compiled and stored in the database as a schema object for repeated execution. A procedure stored in the database is referred to as a stored procedure. Procedures promote reusability and maintainability. When validated, they can be used in any number of applications. If the functional requirements of the application change, only the procedure needs to be updated.

  • Function: A function is a named PL/SQL block that can accept parameters and be invoked. Generally, a function is used to compute a value. A function is similar to a procedure except that a function must return a value to the calling environment, whereas a procedure may or may not return values to its calling environment. Like a procedure, a function has a header, a declarative part, an executable part, and an optional exception-handling part. A function must have a RETURN clause in the header and at least one RETURN statement in the executable section.

    Functions can be stored in the database as a schema object for repeated execution. A function stored in the database is referred to as a stored function. Functions can also be created at client-side applications. Functions promote reusability and maintainability. They can be used in any number of applications. If the processing requirements of an application change, only the function needs to be updated.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-the-structure-of-a-plsql-block.html/feed 0 What is DML? http://www.ucertify.com/article/what-is-dml.html http://www.ucertify.com/article/what-is-dml.html#comments Sun, 12 Jul 2009 00:00:00 +0000 uCertify 1501031

Data Manipulation Language (DML) is a category of SQL statements that query and update data in a database. Statements such as SELECT, UPDATE, INSERT, DELETE etc., are included in this category. These statements can be grouped with Data Control Language (DCL) statements.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-dml.html/feed 0 What is PL/SQL? http://www.ucertify.com/article/what-is-plsql.html http://www.ucertify.com/article/what-is-plsql.html#comments Sat, 11 Jul 2009 00:00:00 +0000 uCertify 1501025

PL/SQL is an extension of Oracle’s procedural language. It combines SQL with the structured programming language constructs, such as IF…THEN, WHILE, LOOP etc. Applications can send PL/SQL blocks to the database instead of sending individual SQL statements. This reduces network traffic.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-plsql.html/feed 0 What is GROUP BY clause? http://www.ucertify.com/article/what-is-group-by-clause.html http://www.ucertify.com/article/what-is-group-by-clause.html#comments Thu, 18 Jun 2009 00:00:00 +0000 uCertify 2442

The GROUP BY clause groups selected rows on the basis of values of specified column(s) for each row, and returns a single row of summary information for each group. Rows that have the same values in the specified grouping column(s) are grouped together. The GROUP BY clause suppresses duplicate rows for the grouping column(s). It does not guarantee the order of the result set. Therefore, an ORDER BY clause should be used with the GROUP BY clause to sort the result set in the desired order.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-group-by-clause.html/feed 0 What is HAVING clause? http://www.ucertify.com/article/what-is-having-clause.html http://www.ucertify.com/article/what-is-having-clause.html#comments Thu, 18 Jun 2009 00:00:00 +0000 uCertify 2474

The HAVING clause sets conditions for the GROUP BY clause in a SELECT statement. It restricts the groups of rows on the basis of aggregate information. Only groups of rows, which satisfy the conditions specified in the HAVING clause are displayed. The HAVING clause cannot be used without an associated GROUP BY clause.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-having-clause.html/feed 0 What is normalization? http://www.ucertify.com/article/what-is-normalization.html http://www.ucertify.com/article/what-is-normalization.html#comments Thu, 18 Jun 2009 00:00:00 +0000 uCertify 1320

Normalization is the method used to optimize databases. It is important to implement a reasonable level of normalization by creating more tables that contain fewer columns and by defining a relationship between the tables. Normalizing a logical database design involves use of formal methods to separate the data into multiple, related tables. These methods are called normalization rules.

Share/Bookmark]]> http://www.ucertify.com/article/what-is-normalization.html/feed 0 What is SUBSTR function? http://www.ucertify.com/article/what-is-substr-function.html http://www.ucertify.com/article/what-is-substr-function.html#comments Wed, 17 Jun 2009 00:00:00 +0000 uCertify 2363

The SUBSTR function returns a specific portion of a character string.

Syntax:

SUBSTR (<str>, <m>[, <n>])

where,

  • str is a character string.

  • m and n are integers.

    • The SUBSTR function returns a portion of str, which is n characters long, starting from position m. If m is positive, the position is counted from the beginning of the string. If m is negative, the position is counted backwards from the end of the string. If m is 0, it is treated as 1. If n is omitted, the function returns all the characters to the end of the string. The function returns NULL if n is 0 or negative.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-substr-function.html/feed 0     What is NVL function? http://www.ucertify.com/article/what-is-nvl-function.html http://www.ucertify.com/article/what-is-nvl-function.html#comments Wed, 17 Jun 2009 00:00:00 +0000 uCertify 2366

    The NVL function is used when a non-NULL value needs to be returned in place of a NULL value.

    Syntax:

    NVL (p1, p2)

    The NVL function takes two arguments, p1 and p2. It returns p2 if p1 is NULL. If p1 is not NULL, the function returns p1 itself.

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-nvl-function.html/feed 0     What is self join? http://www.ucertify.com/article/what-is-self-join.html http://www.ucertify.com/article/what-is-self-join.html#comments Sun, 15 Mar 2009 00:00:00 +0000 uCertify 2483

    Self join joins a table to itself. Each row of the table is joined with itself and with every other row of the table.

    Example:

    SELECT F.EmployeeID, F.LastName, S.EmployeeID, S.LastName, F.Country
    FROM Employee F, Employee S
    WHERE F.Country = S.Country
    AND F.EmployeeID < S.EmployeeID
    ORDER BY F.EmployeeID, S.EmployeeID;

    Share/Bookmark]]>     http://www.ucertify.com/article/what-is-self-join.html/feed 0     What is cardinality? http://www.ucertify.com/article/what-is-cardinality_1501017.html http://www.ucertify.com/article/what-is-cardinality_1501017.html#comments Mon, 10 Sep 2007 00:00:00 +0000 uCertify 1501017 Pass Oracle oca-dba9i-pl-sql - OCA DBA 9i PL/SQL -->

    Cardinality refers to the number of distinct values. For example, if a table has a cardinality of 500, it has 500 columns. Similarly, if a column has a cardinality of 20, it has 20 distinct values.

    Click here to download oracle-pl-sql test study guide and practice question. Download practice question and study guide for 1Z0-001 for exam. Share/Bookmark]]>     http://www.ucertify.com/article/what-is-cardinality_1501017.html/feed 0