Common PL/SQL Interview Questions and Answers

Top PL/SQL Interview Questions and Answers

1. What are some of the limitations of SQL, and how can PL/SQL overcome these?

Some limitations of SQL are:-

• SQL can't make decisions, loop, or branch.
• Because the SQL queries are sent to the Oracle engine at the same time, the speed of execution slows down when there is more traffic.
• During data manipulation, there is no way to check for mistakes.

PL/SQL was made to fix these limitations by keeping what was good about SQL and combining it with procedural commands. It is made as a block-structured language, and the statements in each block are sent to the Oracle engine. This makes processing faster by reducing the amount of traffic.

2. What are some features of PL/SQL?

PL/SQL is made up of the following things:

• PL/SQL can make decisions, loop, and branch because it is a procedural language.
• A single PL/SQL query can handle multiple queries in a single block.
• Since functions, procedures, packages, triggers, and types can be saved as PL/SQL units in databases, applications can reuse the code.
• PL/SQL lets you handle errors by putting them in a block called "exception handling."
• In addition to handling exceptions, PL/SQL lets you check for errors and ensure the data is correct before processing it.
• PL/SQL applications can run on any computer hardware or operating system.

3. What do you know about PL/SQL tables?

PL/SQL tables are objects of type tables that are made to look like database tables. PL/SQL tables give us a way to supply arrays. Arrays are like temporary tables stored in memory and processed very quickly. PL/SQL tables send a lot of data at once. They make it easier to send data sets.

4. Explain how PL/SQL is put together at its core.

BLOCK-based is the basic way PL/SQL is put together. Each PL/SQL code block comprises a SQL statement and a PL/SQL statement. There are three parts to each PL/SQL block:

• Declaration Section
• Execution Section
• Optional Exception management Section

5. What is a cursor in PL/SQL?

A PL/SQL cursor is just a pointer to a place in memory where SQL statements and processing metadata are kept. This part of memory is called the context area. In this area, you can use the cursor to get information from more than one row and look at it. In short, the cursor chooses a few rows from the database, and the programme handles each row separately. 

6. What are the types of cursors?

There are two types of cursors:

Implicit Cursor:

• When you run any of the following commands: SELECT INTO, INSERT, DELETE, or UPDATE, Oracle will automatically make a cursor.
• Oracle handles the execution cycle of these cursors on its own, and the cursor attributes ROWCOUNT, ISOPEN, FOUND, and NOTFOUND are used to get the cursor's information and status.

Explicit Cursor:

• This cursor is a SELECT statement declared in the declaration block.
• The programmer must take care of these cursors' entire life cycle, from OPEN to FETCH to shut.
• Oracle sets up the execution cycle during the execution of a SQL statement and links it to a cursor.

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7. Is Oracle Server necessary to run PL/SQL commands?

The PL/SQL engine can only compile and run PL/SQL blocks and programmes if installed on an Oracle server or an application tool that is compatible with Oracle, like Oracle Forms.

8. Is PL/SQL based on client-server architecture?

Oracle RDBMS includes PL/SQL, and it's important to know that most Oracle applications are built with a client-server architecture. The Oracle database is on the server side, and database requests are on the client-side. Since PL/SQL is not a standalone programming language, we can conclude that the PL/SQL engine can live in either the client or server context. This makes it easier for server-side and client-side applications to use PL/SQL modules and subprograms.

9. Is PL/SQL on the client-side or server-side?

The PL/SQL can be on either side:-

1. Server-side- When the PL/SQL engine is on the server-side, the entire PL/SQL block is sent to the PL/SQL engine on the Oracle server, which then processes it and sends the response.
2. Client-side- When the PL/SQL engine is on the client-side, the engine is part of the Oracle Developer tools, and PL/SQL statements are processed on the client-side. Any SQL statements in the PL/SQL block are sent to the Oracle server so they can be processed. The client does all of the block processing when there are no SQL statements.

10. What does the term "exception handling" mean?

Exception handling is a way to deal with errors during runtime. PL/SQL gives the exception block that causes the error, making it easier for the programmer to find the error and fix it. When a mistake happens, the software has code to deal with it. In PL/SQL, there are two different kinds of exceptions:

• Exception created by the user
• Exception imposed by the system

11. What is the meaning of Expressions?

Expressions are made up of a list of literals and variables separated by operators. PL/SQL use operators to alter, compare, and calculate data. 

12. Explain the Uses of Cursor.

It is possible to access SQL data through a cursor, which is a named private area. For queries that return many rows, they must process each row one at a time.

13. Describe the Functions of Database Triggers.

A PL/SQL program unit linked to a specific database table is a database trigger. What can it do?

• Ensure that data changes are properly audited
• Keep track of everything that happens clearly and concisely
• You must enact complex corporate regulations
• Maintaining a copy of a table
• Calculate the column values
• Design and implement complex security permissions

14. Differentiate between Syntax and Runtime Errors.

A PL/SQL compiler can readily identify a syntax error. For example, a misspelled word.

A PL/SQL block's exception-handling section is responsible for addressing runtime errors. For example, a SELECT INTO command that returns 0 records.

15. Explain Mutating Table Error.

To avoid this problem, the trigger should not attempt to alter the row it is currently utilizing. Using views or temporary tables, the database selects one and then updates the other. Therefore the problem is solved.

16. What Significance Do SQLCODE and SQLERRM Have?

SQLERRM returns the message for the latest error, whereas SQLCODE returns the number of errors encountered.

17. Explain Polymorphism in PL SQL.

Polymorphism plays a role in OOP. A multi-form variable, object, or function can take many different shapes. Polymorphism in PL/SQL is supported by overloading program units within a member function/package. While overloading, it's important to avoid using unambiguous logic.

18. What is a Join?

One or more tables or views are joined to produce a single result set. When there are many tables in the FROM clause of a query, Oracle does a join. From or where most of these queries have at least one join condition.

19. What is a View?

Table joins are used to construct a view. There are rows and columns just as in a real table because it is based on the results of a SQL statement. You can set up a new table or view in SQL with the CREATE VIEW statement.

20. What are the Benefits of PL/SQL Packages?

PL/SQL packages offer a number of advantages. There are a few examples, including:

• Top-down Design: Before implementing the modules, we can design the interface to the code buried within the package.
• Performance Improvement: The RDBMS automatically keeps track of the validity of all program objects in the database. It also helps packages run faster.
• Guaranteeing Transaction Integrity: It ensures a certain amount of transaction integrity by providing a guarantee.
• Enforced Information Hiding: This allows users to decide whether or not they want their data to be made public or private.
• Object Persistence: A package specification's objects are treated as global data for all PL/SQL objects within the application. Modifications to the package can be made in one module, then referenced in another.
• Object-oriented Design: With the package, developers have complete control over how the modules and data structures contained within it can be employed.

21. What is the Difference among Functions, Procedures, and Packages in PL/SQL?

• Functions: PL/SQL functions get designed to calculate and return a single value. Specified values must be returned by all of the tasks in their specifications.
• Procedures: When calling a process, the caller returns to where the system left off. Hence there is no need for a return type for procedures. Policies are similar to functions in that they can return multiple values.
• Packages: Schema objects that aggregate logically similar PL/SQL types, elements, and subprograms into a single package. Packages can be described as a collection of functions, procedures, variables, & record TYPE statements. The modularity provided by packages facilitates the creation of applications. 

FAQs

1. What is PL/SQL? 

PL/SQL is a procedural language with the procedural programming constructs like the iteration, conditional branching, etc., along with the interactive SQL codes. 

2. What is the average salary of PL/SQL developers in India?

As per Glassdoor India, the average salary of a PL/SQL developer is Rs 7,13,191 per year. 

3. What are the top firms that recruit PL/SQL developers?

The top firms include TCS, Cognizant, Accenture, Capgemini, Wipro, Oracle, etc. 

4. What is PL/SQL used for?

PL/SQL is basically used for:

1. Multiple applications can access and share the same subprograms thanks to PL/SQL.
2. Code can be performed on any operating system, as long as Oracle is installed, thanks to PL/SQL’s well-known portability.
3. With the Oracle data dictionary integrated, transaction performance has improved.
4. PL/SQL programmers can create their error handling routines.

5. What is the difference between SQL and PL/SQL?

• SQL is a query language designed for manipulating relational databases. It is a detail-oriented, declarative language. PL/SQL, on the other hand, is a Procedural Language/Structured Query Language whose database is SQL. This language is application-oriented.
• Compared to PL/SQL, SQL does not have variables or data types.
• SQL has direct access to the database server, unlike PL/SQL.

6. What are the features of PL/SQL?

• In PL/SQL, procedural languages are combined with SQL's ability to manipulate data.
• If you know how to solve a problem in SQL, you don't need to learn any new APIs to issue SQL statements from your PL/SQL program.
• PL/SQL allows you to declare constants and parameters, control program flow, define modules, and catch runtime errors, similar to other procedural programming languages.
• It is possible to decompose complex issues into subprograms that can be reused in other applications.

7. What are the data types in PL/SQL?

PL/SQL has a wide variety of data types. They're:

• Scalar: In computing, scalar refers to a one-dimensional data type with no internal elements. Scalar data types include CHAR, DATE, LONG, VARCHAR2, NUMBER, and BOOLEAN.
• Composite: It comprises many data types that are fully customizable and include internal components that may be employed and updated simultaneously, like RECORD, TABLE, and VARRAY.
• Reference: Pointers to other programs or data components are stored in the reference data type. The REF CURSOR exemplifies the reference data type.
• Large Object: Video clips, graphic graphics, and so on are all examples of massive objects that you can store out of line in the large object data type. Large object data types include BLOB, BFILE, CLOB, and NCLOB.

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Conclusion

PL/SQL developer is a nice career option; the interview questions and answers can help you prepare for the interviews. Clearing an interview is the first step to starting your PL/SQL developer career. You should learn the basics and practice several PL/SQL interview questions to prepare for your dream job. Check out Simplilearn’s SQL Training Certification Course which can help you master basic SQL skills and improve your career skills.

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