Interview Questions On Pl Sql For 5 Years Experience
Suggested Interview Questions for 5 Years of PL/SQL Experience
Interview Questions On Pl Sql For 5 Years Experience
In an interview for a PL/SQL developer with five years of experience, you can expect questions that range from advanced SQL queries to stored procedures, functions, triggers, and performance tuning. Expect questions that dive deep into your understanding of database design principles, indexing strategies, and optimization techniques. You may also be asked about your experience in writing complex queries, handling exceptions, and working with larger datasets. Be prepared to discuss your experience with writing efficient and scalable PL/SQL code, as well as your knowledge of best practices and industry standards. Overall, the interview is likely to test your technical expertise in PL/SQL programming and your ability to solve complex problems related to database management and performance.
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1 - Describe the differences between a function and a procedure in PL/SQL.
A function in PL/SQL returns a single value, whereas a procedure does not return any value but may have one or more OUT parameters through which it can pass values back to the caller. Functions are typically used to perform calculations and return a single value, while procedures are used to perform operations that may not necessarily have a return value.
2) Explain the use of cursors in PL/SQL and provide examples.
Cursors in PL/SQL are used to process rows returned by a SQL query one at a time. They can be either explicit or implicit. Explicit cursors are defined and managed by the programmer using DECLARE, OPEN, FETCH, and CLOSE statements, while implicit cursors are automatically created by Oracle when a SELECT statement is executed. An example of an explicit cursor is:
```sql
DECLARE
CURSOR c1 IS SELECT * FROM employees;
emp_record c1%ROWTYPE;
BEGIN
OPEN c1;
LOOP
FETCH c1 INTO emp_record;
EXIT WHEN c1%NOTFOUND;
process the record
END LOOP;
CLOSE c1;
END;
```
3) How do you handle exceptions in PL/SQL? Give examples.
Exceptions in PL/SQL are managed using exceptions blocks where specific exceptions or error conditions can be caught and handled. The EXCEPTION block follows the main executable block and can include WHEN clauses to handle specific exceptions. For example:
```sql
DECLARE
result NUMBER;
BEGIN
SELECT 100/0 INTO result FROM dual;
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EXCEPTION
WHEN ZERO_DIVIDE THEN
DBMS_OUTPUT.PUT_LINE('Error: Division by zero');
END;
```
4) Discuss the difference between TRIGGERS and STORED PROCEDURES in PL/SQL.
Triggers in PL/SQL are special types of stored procedures that are automatically fired or executed when certain events occur in a database table, such as INSERT, UPDATE, DELETE operations. They are attached to tables and are invoked implicitly. On the other hand, stored procedures are user defined routines that are explicitly called by application programs to perform specific tasks or operations.
5) How can you optimize PL/SQL performance?
PL/SQL performance can be optimized by using proper indexing on tables, minimizing the use of context switches between SQL and PL/SQL, avoiding unnecessary loops and cursor iterations, using bulk processing for handling large volumes of data, and optimizing SQL queries by using proper hints and indexing strategies.
6) Explain the difference between implicit and explicit data type conversion in PL/SQL.
Implicit data type conversion in PL/SQL is automatically performed by Oracle when operands in expressions have different data types, and it takes place without the programmer's intervention. Explicit data type conversion, on the other hand, is done explicitly using conversion functions such as TO_NUMBER, TO_DATE, TO_CHAR, etc., to convert data from one type to another.
7) Discuss the concept of collections in PL/SQL and provide examples of different types of collections.
Collections in PL/SQL are variables that can hold multiple values. There are three types of collections: associative arrays (or index by tables), nested tables, and VARRAYs (variable size arrays). Associative arrays use a key value pair mechanism, nested tables are like one dimensional arrays, and VARRAYs have a predefined size. An example of a nested table declaration:
```sql
TYPE EmpTable IS TABLE OF employees%ROWTYPE;
emp_rec EmpTable;
```
8) How do you handle bulk processing in PL/SQL?
Bulk processing in PL/SQL allows you to process multiple rows of data at once, improving performance significantly compared to processing rows one by one. This can be achieved using BULK COLLECT and FORALL statements. BULK COLLECT is used to fetch data from a cursor into a collection, while FORALL is used to perform DML operations on collections in a single step.
9) Explain the use of packages in PL/SQL and the benefits they provide.
Packages in PL/SQL are schema objects that contain related procedures, functions, variables, cursors, and other PL/SQL constructs. They provide modularity, encapsulation, and reusability by grouping related functionalities together. Additionally, packages help in managing dependencies and controlling access to the encapsulated objects.
10) Describe the difference between a trigger and a constraint in PL/SQL.
Triggers in PL/SQL are database objects that are executed automatically in response to specific events on a table, such as INSERT, UPDATE, DELETE operations. On the other hand, constraints are rules or conditions that are defined on a table to enforce data integrity, such as NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY constraints. Triggers are procedural in nature, while constraints are declarative.
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