PL/SQL Interview Questions and Answers: PL/SQL (Procedural Language/Structured Query Language) is an extension of SQL that is commonly used for writing stored procedures, functions, and triggers in Oracle databases. If you’re preparing for a PL/SQL interview, it’s important to have a strong grasp of the technology and the various techniques for managing and manipulating data. To help you prepare for your interview, we have compiled a comprehensive list of the Top 100 PL/SQL Interview Questions and Answers.
★★ Latest Technical Interview Questions ★★
Latest PL/SQL Interview Questions
This list includes the latest PL/SQL interview questions, as well as PL/SQL technical interview questions and PL/SQL interview questions for freshers. By reviewing these questions and answers, you will be better equipped to showcase your knowledge and expertise during your PL/SQL interview and increase your chances of landing your dream job in the field of database management.
Top 100 PL/SQL Interview Questions and Answers 2023
1. What is PL/SQL?
Answer: PL/SQL stands for Procedural Language/Structured Query Language, a procedural programming language designed specifically for Oracle Database management.
2. What are the advantages of using PL/SQL?
Answer:
- PL/SQL is designed specifically for Oracle Database management and provides better performance, scalability, security, and reliability compared to other programming languages.
- PL/SQL also provides a better way to encapsulate business logic, allowing for easier maintenance and reusability of code.
3. What are the features of PL/SQL?
- PL/SQL, with its procedural nature, allows for decision making, looping, and branching. It also provides the capability to process multiple queries using a single command within a block.
- PL/SQL units, such as functions, procedures, packages, triggers, and types, can be grouped and stored in databases, enabling code reuse by applications.
- PL/SQL supports exception handling through the use of dedicated blocks, allowing for error checking and data validation before manipulation.
- Applications created using PL/SQL can be easily ported across different hardware or operating systems, as long as there is an Oracle engine present.
4. Explain the basic structure followed in PL/SQL?
- PL/SQL code follows the BLOCK structure and includes SQL and PL/SQL statements.
- Each PL/SQL block has three sections: Declaration Section (optional), Execution Section (mandatory), and Exception Handling Section (optional).
- The Declaration Section declares variables, cursors, and subprograms used in the block.
- The Execution Section contains the actual PL/SQL statements and SQL queries that perform the desired operations.
- The Exception Handling Section handles any errors or exceptions that may occur during execution.
- The Declaration Section is optional because not all blocks require the declaration of variables or subprograms.
- The Execution Section is mandatory because it contains the core logic of the program and is required for the block to execute.
- The Exception Handling Section is optional but recommended to handle errors and exceptions gracefully.
| [DECLARE] –declaration statements (optional) BEGIN –execution statements [EXCEPTION] –exception handling statements (optional) END; |
5. Explain the PL/SQL execution architecture
- The PL/SQL engine is responsible for compiling and executing PL/SQL blocks and programs.
- It requires an Oracle server or an application tool that supports Oracle, such as Oracle Forms, to function.
- PL/SQL is a component of Oracle RDBMS, and many Oracle applications are developed using client-server architecture.
- The Oracle database forms the server-side, and client requests are sent to the database.
- PL/SQL is not a standalone programming language and can reside in either the client or server environment.
- This allows for easy movement of PL/SQL modules and sub-programs between client-side and server-side applications.
- The PL/SQL engine is critical to the execution process and executes PL/SQL statements, sending SQL statements to the SQL Statement Processor when encountered.
- The architecture illustrates the role of the PL/SQL engine in the process.
- The PL/SQL engine can reside on either the server or client-side.
- In Case 1, where the engine is on the server, the entire PL/SQL block is passed to the server’s PL/SQL engine for processing, and the response is sent back.
- In Case 2, the engine is on the client-side, and processing occurs within Oracle Developer tools.
- If the PL/SQL block includes SQL statements, they are sent to the Oracle server for processing.
- When there are no SQL statements, processing occurs entirely on the client-side.
- The location of the PL/SQL engine affects the processing of the PL/SQL block.
- The choice of whether to use server or client-side processing depends on factors such as network latency and data security.
6. What are the basic components of PL/SQL?
Answer: The basic components of PL/SQL are variables, constants, data types, control structures, procedures, functions, and packages.
7. How do you declare a variable in PL/SQL?
Answer: Variables are declared using the syntax:
| variable_name data_type; |
8. What is the difference between a function and a procedure in PL/SQL?
Answer:
- A function returns a value while a procedure does not.
- Functions can be used in SQL queries, whereas procedures cannot.
9. What are packages in PL/SQL?
Answer: A package is a collection of related procedures, functions, variables, and other PL/SQL constructs that can be used as a single unit. Packages are useful for encapsulating complex business logic and improving performance by reducing the amount of data sent between the database and the application.
10. What is the difference between a mutating table and a constraining table?
- One may refer to a table that is being modified using a DML statement as a “mutating table,” which can also apply to a table that has defined triggers.
- On the other hand, a table that is utilized for reading and enforcing referential integrity constraints is known as a “constraining table.”
11. What is a cursor in PL/SQL?
Answer: A cursor is a database object that allows you to manipulate data row by row. Cursors are used in PL/SQL to retrieve data from a database table or result set, and then process it in a procedural manner.
12. What is dynamic SQL in PL/SQL?
Answer: Dynamic SQL is a technique in PL/SQL that allows you to construct SQL statements at runtime, based on user input or other variables. Dynamic SQL can be useful for building flexible and adaptable applications.
13. What is the difference between SQL and PL/SQL?
| SQL | PL/SQL |
| A single query or command execution | A full programming language |
| A data source for reports, web pages, etc. | An application language to build, format, and display reports, web pages, etc. |
| Declarative in nature | Procedural in nature |
| Manipulating data | Creating applications |
14. What is a deadlock in PL/SQL?
Answer: A deadlock is a situation where two or more transactions are waiting for each other to release locks on database objects. Deadlocks can be prevented or resolved by using appropriate locking strategies and transaction isolation levels.
15. How do you assign a value to a variable in PL/SQL?
Answer: To assign a value to a variable, use the syntax:
| variable_name := value; |
16. What is the difference between a primary key and a unique key in PL/SQL?
Answer:
- A primary key is a column or set of columns that uniquely identifies each row in a table, and is used to enforce referential integrity.
- A unique key is similar to a primary key, but does not necessarily enforce referential integrity.
17. What is a synonym in PL/SQL?
Answer: A synonym is an alternative name for a database object, such as a table, view, or stored procedure. Synonyms can be useful for simplifying SQL queries and improving readability.
18. What data types are present in PL/SQL?
PL/SQL supports several data types, including scalar, composite, reference, and large object data types.
- Scalar data types are one-dimensional and have no internal components. Examples include CHAR, DATE, LONG, VARCHAR2, NUMBER, and BOOLEAN.
- Composite data types are made up of different data types and are easy to update. They have internal components that can be modified together. Examples include RECORD, TABLE, VARRAY, and more.
- Reference data types store pointers, which are values that relate to other programs or data elements. An example is REF CURSOR.
- Large Object data types store locators that define the location of large items stored out of line, such as video clips and graphic images. Examples include BLOB, BFILE, CLOB, and NCLOB.
19. What is the difference between a view and a materialized view in PL/SQL?
Answer:
- A view is a virtual table that is created by a SELECT statement, and does not physically exist in the database.
- A materialized view is a physical copy of a view that is stored in the database and is updated periodically to reflect changes in the underlying data.
20. What is the difference between a VARCHAR2 and a CHAR data type in PL/SQL?
Answer:
- VARCHAR2 is a variable-length string data type that can store up to 32767 characters.
- CHAR is a fixed-length string data type that always stores a specific number of characters, and pads the remaining space with blanks.
21. What is the difference between an IN and OUT parameter in PL/SQL?
Answer:
- An IN parameter is a parameter that is passed into a PL/SQL block or subprogram for processing.
- An OUT parameter is a parameter that is returned from a PL/SQL block or subprogram after processing.
22. How do you declare a constant in PL/SQL?
Answer: Constants are declared using the syntax:
| CONSTANT constant_name data_type := value; |
23. What is a sequence in PL/SQL?
Answer: A sequence is a database object that generates a sequence of unique numbers, which can be used as primary keys or other identifiers. Sequences can be useful for generating unique values for large-scale applications.
24. What does a PL/SQL Package consist of?
Answer: A PL/SQL package consists of:
- PL/SQL table and record type statements
- Variables, such as tables, scalars, records, etc., and constants
- Exception names and pragmas for relating an error number with an exception
- Procedures and functions
- Cursors
- Cursors
25. What is a database trigger in PL/SQL?
Answer: A database trigger is a piece of code that is automatically executed in response to certain events or actions in a database, such as a row being inserted, updated, or deleted. Database triggers can be used to enforce business rules, maintain data integrity, and automate complex database operations.
26. What are the Benefits of PL/SQL Packages?
- PL/SQL offers enforced information hiding, allowing developers to choose whether to keep data private or public.
- Top-down design is possible in PL/SQL, enabling the interface to the code hidden in the package to be designed before the modules are implemented.
- PL/SQL offers object persistence, where objects declared in a package specification behave like global data for all PL/SQL objects in the application. Changes made to the package in one module can be referenced in another.
- Object-oriented design is facilitated by the package construct in PL/SQL, which gives developers control over how modules and data structures within the package can be used.
- PL/SQL provides a certain level of transaction integrity, guaranteeing consistency and atomicity for database operations.
- The RDBMS automatically tracks the validity of all program objects stored in the database, enhancing the performance of packages and improving overall system performance.
27. How do you declare a cursor in PL/SQL?
Answer: Cursors are declared using the syntax:
| CURSOR cursor_name IS SELECT column1, column2, … FROM table_name WHERE condition; |
28. What is a cursor for loop in PL/SQL?
Answer: A cursor for loop is a type of loop that is used in PL/SQL to iterate over the rows of a result set or database table. Cursor for loops can simplify the process of retrieving and processing data in PL/SQL, and can improve performance by reducing the amount of code required.
29. What is a pragma in PL/SQL?
Answer: A pragma is a compiler directive that provides additional information to the PL/SQL compiler, such as optimization hints or warnings. Pragmas can be useful for improving performance, optimizing code, or enforcing coding standards.
30. How do you open a cursor in PL/SQL?
Answer: To open a cursor, use the syntax:
| OPEN cursor_name; |
31. What is a REF CURSOR in PL/SQL?
- A REF CURSOR is a cursor that is defined in a PL/SQL block or subprogram, and can be passed as a parameter to another PL/SQL block or subprogram.
- REF CURSORS can be useful for building flexible and adaptable applications that can dynamically generate SQL queries.
32. What are the differences between the implicit cursor and explicit cursor?
Answer:
| Implicit Cursor | Explicit Cursor |
|---|---|
| An implicit cursor is used when a query returns a single row value. | When a subquery returns more than one row, an explicit cursor is used. These rows are called Active Set. |
| NO_DATA_FOUND Exception is handled here. | NO_DATA_FOUND cannot be handled here. |
| This is used for all DML operations like DECLARE, OPEN, FETCH, CLOSE. | This is used to process Multirow SELECT Statements. |
33. What is a bind variable in PL/SQL?
Answer: A bind variable is a placeholder in a SQL statement that is replaced with a value at runtime. Bind variables can improve performance and security by reducing the amount of SQL parsing required and preventing SQL injection attacks.
34. What is a FORALL statement in PL/SQL?
Answer: A FORALL statement is a PL/SQL construct that allows you to perform bulk operations on a collection or database table. FORALL statements can significantly improve performance by reducing the number of context switches between the database and the application.
35. How do you fetch data from a cursor in PL/SQL?
Answer: Data can be fetched from a cursor using the syntax:
| FETCH cursor_name INTO variable1, variable2, …; |
36. What is a hash function in PL/SQL?
Answer: A hash function is a function that takes a variable-length input and produces a fixed-length output, called a hash value or hash code. Hash functions can be useful for indexing and searching large data sets, and can provide a way to verify the integrity of data.
37. What is a trigger-based audit trail in PL/SQL?
Answer: A trigger-based audit trail is a technique in PL/SQL that uses database triggers to automatically record changes to database objects. Trigger-based audit trails can be useful for tracking changes to sensitive data and enforcing data retention policies.
38. What is the difference between an EXCEPTION and a RAISE statement in PL/SQL?
Answer:
- An EXCEPTION statement is used to handle errors or exceptions that occur during the execution of a PL/SQL block or subprogram.
- A RAISE statement is used to generate an error or exception in a PL/SQL block or subprogram, which can then be handled by an EXCEPTION statement or propagated up the call stack.
39. What is a user-defined exception in PL/SQL?
Answer: A user-defined exception is an exception that is defined by the user in PL/SQL code. User-defined exceptions can be useful for customizing error handling and improving the readability and maintainability of PL/SQL code.
40. What are the Advantages of Stored Procedures?
Answer: Advantages of Stored Procedures are
- Better performance
- Ease of use
- Increased scalability
- Interoperability
- Higher productivity
- Advance security
- Replication
41. What is a subprogram in PL/SQL?
Answer: A subprogram is a named PL/SQL block that can be called from other PL/SQL blocks or subprograms. Subprograms can help to modularize PL/SQL code, reduce redundancy, and improve code reusability.
42. How do you close a cursor in PL/SQL?
Answer: To close a cursor, use the syntax:
| CLOSE cursor_name; |
43. What is an autonomous transaction in PL/SQL?
Answer: An autonomous transaction is a transaction that is independent of the calling transaction in PL/SQL. Autonomous transactions can be useful for implementing logging, auditing, or error handling functionality in PL/SQL code.
44. What is a bulk collect in PL/SQL?
Answer: A bulk collect is a feature in PL/SQL that allows you to fetch multiple rows from a cursor or query into a collection in a single operation. Bulk collect can significantly improve performance by reducing the number of context switches between the database and the application.
45. How do you declare a procedure in PL/SQL?
Answer: Procedures are declared using the syntax:
| PROCEDURE procedure_name IS BEGIN … END; |
46. What is a SQL injection attack?
Answer: A SQL injection attack is a type of security exploit in which an attacker injects malicious SQL code into a database query, with the goal of stealing data or compromising the security of a system. SQL injection attacks can be prevented by using bind variables, input validation, and other security best practices.
47. What is the difference between a scalar and a composite data type in PL/SQL?
Answer:
- A scalar data type is a single value, such as a number or string.
- A composite data type is a collection of values, such as an array or record.
48. How do you declare a function in PL/SQL?
Answer: Functions are declared using the syntax:
| FUNCTION function_name RETURN return_data_type IS BEGIN … END; |
49. What is a NOCOPY hint in PL/SQL?
Answer: A NOCOPY hint is a compiler directive that instructs the PL/SQL compiler to pass a large variable by reference instead of by value. NOCOPY hints can improve the performance of PL/SQL code by reducing the amount of memory allocation and copying required.
50. What is a PL/Scope in PL/SQL?
Answer: PL/Scope is a feature in PL/SQL that analyzes the code of a program unit and records information about the identifiers and data types used. PL/Scope can be useful for improving the maintainability and quality of PL/SQL code, and can help to identify potential issues and opportunities for optimization.
51. How do you call a procedure in PL/SQL?
Answer: To call a procedure, use the syntax:
| procedure_name; |
52. What is a package in PL/SQL?
Answer: A package is a named collection of PL/SQL objects, such as subprograms, cursors, and types. Packages can help to modularize PL/SQL code, improve code reuse, and simplify the development, maintenance, and testing of PL/SQL code.
53. How do you call a function in PL/SQL?
Answer: To call a function, use the syntax:
| variable_name := function_name; |
54. What is a database link in PL/SQL?
Answer: A database link is a connection between two Oracle databases that allows you to query and modify data in one database from another database. Database links can be useful for distributed applications, data migration, and other scenarios where you need to access data in multiple databases.
55. What is a VARRAY in PL/SQL?
Answer: A VARRAY is a variable-size array in PL/SQL that can store a collection of values of the same data type. VARRAYs can be useful for storing and processing sets of data efficiently, and can be used in conjunction with other PL/SQL features such as cursor FOR loops and bulk binds.
56. What is a PL/SQL table?
Answer: A PL/SQL table is a type of collection in PL/SQL that can store a set of values of the same data type. PL/SQL tables can be useful for storing and processing sets of data efficiently, and can be used in conjunction with other PL/SQL features such as cursor FOR loops and bulk binds.
57. What is a ref cursor in PL/SQL?
Answer: A ref cursor is a cursor that is dynamically created and opened in PL/SQL code, rather than being explicitly defined in the database. Ref cursors can be useful for dynamic SQL, data manipulation, and other scenarios where you need to process sets of data that are not known at compile time.
58. How do you create a trigger in PL/SQL?
Answer: Triggers are created using the syntax:
| CREATE OR REPLACE TRIGGER trigger_name BEFORE/AFTER INSERT/UPDATE/DELETE ON table_name FOR EACH ROW BEGIN … END; |
59. What is a nested table in PL/SQL?
Answer: A nested table is a type of collection in PL/SQL that can store a set of values of the same data type, similar to a PL/SQL table. Nested tables can be useful for storing and processing sets of data efficiently, and can be used in conjunction with other PL/SQL features such as cursor FOR loops and bulk binds.
60. What is a pipelined function in PL/SQL?
Answer: A pipelined function is a PL/SQL function that returns a set of rows one at a time, rather than returning the entire result set at once. Pipelined functions can be useful for processing large data sets efficiently, and can be used in conjunction with other PL/SQL features such as cursor FOR loops and bulk binds.
61. What is a pragma autonomous_transaction in PL/SQL?
Answer: A pragma autonomous_transaction is a compiler directive that allows you to specify that a PL/SQL block or subprogram should be executed as an autonomous transaction, separate from the calling transaction. Pragma autonomous_transaction can be useful for implementing logging, auditing, or error handling functionality in PL/SQL code.
62. What is a pragma restrict_references in PL/SQL?
Answer:
- A pragma restrict_references is a compiler directive that allows you to specify which PL/SQL units can be referenced by a program unit.
- Pragma restrict_references can be useful for improving the security and maintainability of PL/SQL code, and can help to prevent unauthorized access to sensitive data or functions.
63. How do you insert data into a table in PL/SQL?
Answer: Data can be inserted into a table using the syntax:
| INSERT INTO table_name (column1, column2, …) VALUES (value1, value2, …); |
64. What is the difference between a local and a global temporary table in PL/SQL?
Answer:
- A local temporary table is created and used within the scope of a single session or transaction, and is automatically dropped at the end of the session or transaction.
- A global temporary table is created once and can be used by multiple sessions, but the data in the table is private to each session and is automatically cleared when the session ends.
65. What is an object type in PL/SQL?
Answer:
- An object type is a user-defined data type in PL/SQL that can encapsulate complex data structures and behaviors, similar to a class in object-oriented programming.
- Object types can be useful for modeling real-world entities and relationships, and can be used in conjunction with other PL/SQL features such as inheritance, encapsulation, and polymorphism.
66. What is an abstract data type in PL/SQL?
Answer:
- An abstract data type is a user-defined data type in PL/SQL that defines a set of operations or behaviors, but does not specify how those operations are implemented.
- Abstract data types can be useful for defining a high-level interface for working with data, while allowing the implementation details to be changed or optimized without affecting the external interface.
67. How do you update data in a table in PL/SQL?
Answer: Data can be updated in a table using the syntax:
| UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition; |
68. What is a pragma exception_init in PL/SQL?
Answer:
- A pragma exception_init is a compiler directive that associates an exception name with a specific Oracle error code or condition.
- Pragma exception_init can be useful for handling specific types of errors or exceptions in PL/SQL code, and can help to improve the accuracy and granularity of error handling.
69. What is a trigger-based auditing in PL/SQL?
Answer: A trigger-based auditing is a technique in PL/SQL that uses triggers to capture and log changes to database tables or records, for the purpose of auditing or tracking changes. Trigger-based auditing can be useful for implementing regulatory compliance, ensuring data integrity, and tracking user behavior and activity.
70. What is bulk binding in PL/SQL?
Answer:
- Bulk binding is a technique in PL/SQL that allows you to process sets of data efficiently, by binding multiple rows or elements to a single variable or parameter at once.
- Bulk binding can be useful for improving the performance and scalability of PL/SQL code, and can be used in conjunction with other PL/SQL features such as cursor FOR loops and collections.
71. What is PL/SQL code instrumentation?
Answer: PL/SQL code instrumentation is the process of adding additional code or functionality to PL/SQL code, for the purpose of monitoring, profiling, or debugging. Code instrumentation can be useful for identifying performance bottlenecks, detecting errors or exceptions, and improving the overall quality and maintainability of PL/SQL code.
72. How do you delete data from a table in PL/SQL?
Answer: Data can be deleted from a table using the syntax:
| DELETE FROM table_name WHERE condition; |
73. What is an execution plan in PL/SQL?
Answer:
- An execution plan is a set of instructions that describes how Oracle will execute a SQL statement, including the order of operations, the access paths, and the join methods.
- Execution plans can be useful for understanding and optimizing the performance of SQL queries, and can be generated and analyzed using various PL/SQL tools and utilities.
74. What is a database package in PL/SQL?
Answer:
- A database packageis a collection of related PL/SQL program units, including procedures, functions, variables, constants, and cursors, that can be compiled and stored in the database for reuse.
- Database packages can be useful for encapsulating business logic and data access, improving performance and scalability, and ensuring code consistency and maintainability.
75. How do you declare an exception in PL/SQL?
Answer: Exceptions are declared using the syntax:
| EXCEPTION exception_name; |
76. What is the difference between a stored procedure and a stored function in PL/SQL?
Answer:
- A stored procedure is a PL/SQL program unit that performs a specific task or set of tasks, and may or may not return a value.
- A stored function is a PL/SQL program unit that returns a single value, and may or may not perform additional tasks.
- The main difference between a stored procedure and a stored function is that a function must return a value, whereas a procedure may or may not return a value.
77. What is a cursor variable in PL/SQL?
Answer:
- A cursor variable, also known as a ref cursor, is a data type in PL/SQL that allows you to pass a cursor as a parameter to a procedure or function, or to store it as a variable.
- Cursor variables can be useful for building dynamic and flexible SQL queries, and can be used in conjunction with other PL/SQL features such as bulk binding and dynamic SQL.
78. How do you raise an exception in PL/SQL?
Answer: To raise an exception, use the syntax:
| RAISE exception_name; |
79. What is a cursor FOR loop in PL/SQL?
Answer:
- A cursor FOR loop is a PL/SQL loop statement that implicitly declares and opens a cursor, and then fetches and processes rows from the cursor until there are no more rows.
- Cursor FOR loops can be useful for simplifying the syntax and structure of PL/SQL code, and can be used in conjunction with other PL/SQL features such as bulk binding and cursor variables.
80. What is a package specification in PL/SQL?
Answer: A package specification, also known as a package header, is a PL/SQL program unit that declares the public interface and global variables for a database package. Package specifications can be useful for providing a well-defined and encapsulated interface to a set of related PL/SQL program units, and for allowing other program units to use the package without needing to know the details of its implementation.
81. What is a package body in PL/SQL?
Answer: A package body is a PL/SQL program unit that defines the implementation of a database package, including the private variables, constants, and procedures and functions that are not declared in the package specification. Package bodies can be useful for encapsulating complex logic and data access in a well-organized and modular way, and for providing a stable and efficient interface to other program units.
82. How do you handle an exception in PL/SQL?
Answer: Exceptions can be handled using the syntax:
| BEGIN … EXCEPTION WHEN exception_name THEN … END; |
83. What is the difference between a local and a global variable in PL/SQL?
Answer:
- A local variable is a variable that is declared and used within a specific PL/SQL block, procedure, or function, and has a limited scope and lifetime.
- A global variable is a variable that is declared outside of any specific PL/SQL block, procedure, or function, and has a longer lifetime and a broader scope that may span multiple program units.
84. What is an exception in PL/SQL?
Answer: An exception is an error or unexpected condition that occurs during the execution of a PL/SQL program, and can be handled or propagated using the exception handling mechanism. Exceptions can be useful for handling errors and ensuring program robustness and reliability, and can be customized or defined by the programmer to suit the specific needs of the program.
85. What is the difference between a user-defined and a system-defined exception in PL/SQL?
Answer:
- A user-defined exception is an exception that is defined by the programmer in PL/SQL code using the EXCEPTION keyword, and can be customized to suit the specific needs of the program.
- A system-defined exception is an exception that is predefined by the PL/SQL language or the Oracle database, and typically reflects a specific error condition or limitation of the database.
86. What is the difference between the SQL and PL/SQL languages?
Answer:
- SQL is a declarative language used for querying and manipulating data in a relational database, while PL/SQL is a procedural language used for writing application logic and stored procedures in the database.
- While SQL is primarily used for data retrieval and modification, PL/SQL can handle more complex business logic and application requirements, and can be integrated with other programming languages.
87. How do you declare a sequence in PL/SQL?
Answer: Sequences are declared using the syntax:
| CREATE SEQUENCE sequence_name START WITH value INCREMENT BY value MAXVALUE value; |
88. What is a trigger in PL/SQL?
Answer: A trigger is a PL/SQL program unit that is automatically executed by the database in response to a specific event or action, such as a data modification or a system event. Triggers can be useful for implementing complex business rules, enforcing data integrity, or logging changes to the database.
| TRIGGER trigger_name trigger_event [ restrictions ] BEGIN actions_of_trigger; END; |
89. How do you retrieve the current value of a sequence in PL/SQL?
Answer: To retrieve the current value of a sequence, use the syntax:
| variable_name := sequence_name.CURRVAL; |
90. What is the difference between an IN parameter and an OUT parameter in PL/SQL?
Answer:
- An IN parameter is a parameter that is passed to a PL/SQL program unit, such as a procedure or function, from the calling program unit, and is used for input values or arguments.
- An OUT parameter is a parameter that is passed from a PL/SQL program unit back to the calling program unit, and is used for returning values or results.
91. What is a mutating table error in PL/SQL?
Answer: A mutating table error is an error that occurs in PL/SQL when a trigger or other program unit attempts to modify a table that is currently being modified by another transaction, resulting in an inconsistent or undefined state. Mutating table errors can be difficult to diagnose and resolve, and often require careful design and testing of the program logic and data access patterns.
92. What is the difference between a database procedure and a database function in PL/SQL?
Answer:
- A database procedure is a program unit in PL/SQL that performs a specific task or operation and does not return a value to the caller, and is stored in the database and can be executed by other program units.
- A database function is a program unit in PL/SQL that performs a specific task or operation and returns a value to the caller, and is stored in the database and can be called from other program units or SQL statements.
- While both database procedures and functions can be useful for encapsulating business logic and database operations, functions are typically more flexible and can be used in a wider range of contexts.
93. What is a PL/SQL record?
Answer: A PL/SQL record is a data structure in PL/SQL that represents a single row or record from a database table or view, and consists of a set of fields or attributes. PL/SQL records can be useful for processing individual rows of data, performing data validation and transformation, or passing data between program units.
94. What is the difference between a PL/SQL record and a PL/SQL table?
Answer:
- A PL/SQL record represents a single row or record from a database table or view, while a PL/SQL table represents a collection of rows or values.
- PL/SQL records are typically used for processing individual rows of data, while PL/SQL tables are typically used for processing sets of data.
95. What is the difference between a global temporary table and a permanent table in PL/SQL?
Answer:
- A global temporary table is a database table in PL/SQL that is defined once and can be used by multiple sessions or transactions, but the data in the table is only visible and accessible to the session that created it and its child sessions.
- A permanent table is a database table in PL/SQL that is created and maintained by the database and is visible and accessible to all sessions and transactions.
- Global temporary tables can be useful for temporary storage and processing of data, while permanent tables are typically used for long-term data storage and management.
96. What is a PL/SQL collection?
Answer: A PL/SQL collection is a data structure in PL/SQL that represents a group or collection of related values or objects, such as a list or array. PL/SQL collections can be useful for organizing and processing data, performing aggregate calculations, or storing temporary data during program execution.
97. What are the different types of PL/SQL collections?
Answer:
- There are three main types of PL/SQL collections: associative arrays, nested tables, and VARRAYs.
- Associative arrays are similar to hash tables in other programming languages and allow you to access values using a key instead of an index.
- Nested tables are similar to arrays in other programming languages and allow you to store and process sets of related values.
- VARRAYs are similar to nested tables but have a fixed size that is defined at creation time.
98. What is the difference between a package specification and a package body in PL/SQL?
Answer:
- A package specification in PL/SQL defines the interface or public interface to a database package, including the public variables, constants, procedures, and functions that are available to other program units.
- A package body in PL/SQL contains the implementation or private implementation of a database package, including the private variables, constants, procedures, and functions that are used internally by the package.
99. What is a PL/SQL exception?
Answer: A PL/SQL exception is an error or exception that occurs during program execution and can be handled using exception handling mechanisms. PL/SQL exceptions can be caused by a wide range of factors, including input errors, database errors, and system errors.
100. What is a global temporary table in PL/SQL?
Answer:
- A global temporary table is a database table in PL/SQL that is defined once and can be used by multiple sessions or transactions, but the data in the table is only visible and accessible to the session that created it and its child sessions.
- Global temporary tables can be useful for temporary storage and processing of data, such as during complex data processing tasks or batch jobs.
The comprehensive list of the Top 100 PL/SQL Interview Questions and Answers provides valuable insights for preparing for a PL/SQL interview and showcasing expertise. We encourage you to follow us at freshersnow.com to expand your knowledge and stay updated with the latest information.