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Top Answers to PL-SQL Interview Questions
1.Compare SQL & PL/SQL
|What it is
||Single query or command execution
||Full programming language
|What it comprises
||Data source for reports, web pages
||Application language to build, format and display report, web pages
||Declarative in nature
||Procedural in nature
3.What is the basic structure of PL/SQL?
PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.
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4.Explain the uses of database trigger?
A PL/SQL program unit associated with a particular database table is called a database trigger. It is used for :
- Audit data modifications.
- Log events transparently.
- Enforce complex business rules.
- Maintain replica tables
- Derive column values
- Implement Complex security authorizations
5.How is a process of PL/SQL compiled?
Compilation process includes syntax check, bind and p-code generation processes.Syntax checking checks the PL/SQL codes for compilation errors. When all errors are corrected, a storage address is assigned to the variables that hold data. It is called Binding. P-code is a list of instructions for the PL/SQL engine
. P-code is stored in the database for named blocks and is used the next time it is executed.
6.Mention what PL/SQL package consists of?
A PL/SQL package consists of
- PL/SQL table and record TYPE statements
- Procedures and Functions
- Variables ( tables, scalars, records, etc.) and constants
- Exception names and pragmas for relating an error number with an exception
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7.What are the benefits of PL/SQL packages?
It provides several benefits like
- Enforced Information Hiding: It offers the liberty to choose whether to keep data private or public
- Top-down design: You can design the interface to the code hidden in the package before you actually implemented the modules themselves
- Object persistence: Objects declared in a package specification behaves like a global data for all PL/SQL objects in the application. You can modify the package in one module and then reference those changes to another module
- Object oriented design: The package gives developers strong hold over how the modules and data structures inside the package can be used
- Guaranteeing transaction integrity: It provides a level of transaction integrity
- Performance improvement: The RDBMS automatically tracks the validity of all program objects stored in the database and enhance the performance of packages.
8.What are different methods to trace the PL/SQL code?
Tracing code is a crucial technique to measure the code performance during the runtime. Different methods for tracing includes
- DBMS_SESSION and DBMS_MONITOR
- trcsess and tkproof utilities
9. What is the difference between FUNCTION, PROCEDURE AND PACKAGE in PL/SQL?
: The main purpose of a PL/SQL function
is generally to compute and return a single value. A function has a return type in its specification and must return a value specified in that type.
: A procedure does not have a return type and should not return any value but it can have a return statement that simply stops its execution and returns to the caller. A procedure is used to return multiple values otherwise it is generally similar to a function.
: A package is schema object which groups logically related PL/SQL types , items and subprograms. You can also say that it is a group of functions, procedure, variables and record type statement. It provides modularity, due to this facility it aids application development. It is used to hide information from unauthorized users.
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10.What is stored Procedure?
A stored procedure is a sequence of statement or a named PL/SQL block which performs one or more specific functions. It is similar to a procedure in other programming languages
. It is stored in the database and can be repeatedly executed. It is stored as schema object. It can be nested, invoked and parameterized.
11.What is cursor and why it is required?
A cursor is a temporary work area created in a system memory when an SQL statement is executed.A cursor contains information on a select statement and the row of data accessed by it. This temporary work area stores the data retrieved from the database
and manipulate this data. A cursor can hold more than one row, but can process only one row at a time. Cursor are required to process rows individually for queries.