100+ Plsql Developer Interview Questions and Answers

Primary key uniquely identifies each record in a table, while foreign key establishes a link between two tables.

• Primary key ensures uniqueness and cannot have null values

• Foreign key establishes a relationship between tables based on the primary key of another table

• Example of primary key: EmployeeID in an Employee table

• Example of foreign key: DepartmentID in an Employee table linking to DepartmentID in a Department table

Use a SQL query with GROUP BY and HAVING clause to find duplicate values in a database.

• Use GROUP BY clause to group the values that are duplicated.

• Use HAVING clause to filter out the groups that have more than one occurrence.

• Example: SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name HAVING COUNT(*) > 1;

A trigger is a PL/SQL block that is automatically executed in response to a specific event. A procedure is a named PL/SQL block that performs a specific task. A cursor is a database object used to retrieve data from a result set.

• A trigger is used to automatically execute a set of SQL statements when a specific event occurs, such as inserting, updating, or deleting data from a table.

• A procedure is a reusable block of code that can be called multiple times to perform a specific...read more

SQL optimization, normalization, and pragma usage are important concepts in PL/SQL development.

• SQL optimization involves improving the performance of SQL queries by analyzing and modifying the query structure, indexes, and data access patterns.

• Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.

• Pragma is a compiler directive that provides additional information to the compiler to optimize code performance.

• Examples of p...read more

The query displays employee records with the same salary.

• Use the GROUP BY clause to group the records by salary.

• Use the HAVING clause to filter the groups with more than one employee.

• Select the necessary columns to display the employee records.

Procedures are used to perform an action, while functions return a value.

• Procedures do not return a value, while functions do.

• Functions can be called from SQL queries, while procedures cannot.

• Functions must return a value, while procedures do not necessarily have to.

Editing data in complex views can affect underlying tables, but it depends on the view's structure and rules.

• Complex views often involve joins, aggregations, or groupings, making them non-updatable.

• If a view is updatable, changes made to it will reflect in the underlying tables.

• Example: A simple view on a single table can be updated directly.

• Example: A view that aggregates data (e.g., SUM, COUNT) cannot be updated directly.

• Triggers or INSTEAD OF triggers can be used to manage...read more

Substr function extracts a substring from a string, while Instr function returns the position of a substring within a string.

• Substr function syntax: SUBSTR(string, start_position, length)

• Example: SUBSTR('Hello World', 7, 5) will return 'World'

• Instr function syntax: INSTR(string, substring)

• Example: INSTR('Hello World', 'World') will return 7

A trigger can automate data insertion in response to changes in a specified table.

• Triggers are database objects that automatically execute when a specified event occurs.

• To create a trigger for INSERT, DELETE, or UPDATE, use the CREATE TRIGGER statement.

• Example: CREATE TRIGGER trg_after_insert AFTER INSERT ON source_table FOR EACH ROW INSERT INTO target_table (column1) VALUES (:NEW.column1);

• You can define the timing of the trigger: BEFORE or AFTER the event.

• Triggers can also h...read more

Joins in SQL are used to combine rows from two or more tables based on a related column between them.

• Joins are used to retrieve data from multiple tables based on a related column.

• Common types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

• Example: SELECT * FROM table1 INNER JOIN table2 ON table1.column = table2.column;

A package is a collection of related procedures, functions, variables, and other PL/SQL constructs.

• Packages help organize and encapsulate code for easier maintenance and reuse.

• They can contain both public and private elements.

• Packages can be used to group related functionality together, improving code modularity.

• Example: CREATE PACKAGE my_package AS ... END my_package;

Use a subquery to find the third highest salary in a table.

• Use the RANK() function to assign a rank to each salary in descending order.

• Filter the results to only include rows with a rank of 3.

• Consider handling ties in salaries appropriately.

Triggers are database objects that automatically execute in response to certain events.

• Triggers can be used to enforce business rules, audit data changes, and maintain referential integrity.

• They can be defined to execute before or after an event, such as a row being inserted, updated, or deleted.

• Triggers can also be nested, meaning one trigger can execute another trigger.

• Examples of triggers include automatically updating a timestamp when a row is modified, or preventing a de...read more

A cursor is a database object used to retrieve data from a result set one row at a time.

• Types of cursors: Implicit, Explicit, Ref, and Dynamic

• Implicit cursor is used for single row queries

• Explicit cursor is used for multi-row queries

• Ref cursor is used to point to a cursor variable

• Dynamic cursor is used to execute dynamic SQL statements

Resolved a critical bug causing data loss and implemented a new feature for better user experience.

• Identified root cause of data loss bug by analyzing database queries and logs

• Collaborated with cross-functional teams to prioritize and implement a fix

• Designed and implemented a new feature based on user feedback to enhance usability

A trigger in database management is a special type of stored procedure that is automatically executed when certain events occur in a database.

• Triggers can be used to enforce business rules, maintain referential integrity, and automate repetitive tasks.

• There are two main types of triggers: row-level triggers and statement-level triggers.

• Row-level triggers are fired for each row affected by a triggering statement, while statement-level triggers are fired once for each triggerin...read more

A PL/SQL function to validate email addresses using regex patterns.

• Define a function with a VARCHAR2 parameter for the email address.

• Use regular expressions to match the email format.

• Return TRUE if the email matches the pattern, otherwise FALSE.

• Example regex: '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}$'.

• Consider edge cases like missing '@' or domain parts.

I conducted thorough analysis by reviewing code, logs, and discussing with team members.

• Reviewed code to identify potential issues

• Analyzed logs for error messages and patterns

• Discussed with team members to gather insights and perspectives

• Used debugging tools to trace the root cause

Cursors are used to retrieve and manipulate data from a database in PL/SQL.

• Cursors are like pointers to a result set, allowing us to fetch and process rows one by one.

• There are two types of cursors: implicit and explicit.

• Implicit cursors are automatically created by Oracle when executing a SQL statement.

• Explicit cursors are declared and used by the programmer.

• Explicit cursors provide more control and flexibility compared to implicit cursors.

• Cursors can be used to fetch data f...read more

Procedures and functions are both PL/SQL program units, but they have some key differences.

• Procedures do not return a value, while functions do.

• Procedures can have OUT parameters to pass values back to the caller, while functions cannot.

• Functions can be used in SQL statements, while procedures cannot.

• Functions must return a value, while procedures do not necessarily have to.

• Procedures are typically used for performing actions, while functions are used for calculations or data...read more

Exception handling is a mechanism to handle errors or unexpected events in a program.

• Syntax: BEGIN -- code block EXCEPTION -- exception handling block END;

• Exceptions can be predefined or user-defined

• Common predefined exceptions include NO_DATA_FOUND, TOO_MANY_ROWS, etc.

• User-defined exceptions can be declared using the EXCEPTION keyword

Foreign key, primary key, and unique key are all constraints used in database tables to enforce data integrity.

• Primary key is a column or a set of columns that uniquely identifies each row in a table.

• Foreign key is a column or a set of columns in one table that refers to the primary key in another table.

• Unique key ensures that the values in a column or a set of columns are unique across all the rows in a table.

A cursor is a pointer to a private SQL area that stores information about the processing of a SELECT or DML statement. A trigger is a stored program that is executed automatically in response to certain events or actions.

• A cursor is used to retrieve data from a result set one row at a time

• A trigger can be used to enforce business rules, audit changes to data, or replicate data to other tables

• Triggers can be classified as row-level or statement-level triggers

• Trigger performanc...read more

A dynamic cursor in database management allows for the execution of different SQL queries at runtime.

• Dynamic cursors are used when the SQL query to be executed is not known until runtime.

• They allow for flexibility in querying the database based on user input or other conditions.

• Dynamic cursors can be used to handle varying result sets or conditions in a more efficient manner.

• Example: Using a dynamic cursor to search for different products based on user-selected criteria.

Procedures are used to perform an action, while functions return a value.

• Procedures do not return a value, while functions do.

• Functions can be used in SQL queries, while procedures cannot.

• Functions can be called from within SQL statements, while procedures cannot.

• Procedures can have OUT parameters to return multiple values, while functions can only return a single value.

SQL query to find the nth highest salary

• Use the ORDER BY clause to sort the salaries in descending order

• Use the LIMIT clause to select the nth highest salary

Fetch even numbers from a table while excluding specific values using SQL queries.

• Use the MOD function to filter even numbers: SELECT * FROM table WHERE MOD(column_name, 2) = 0;

• To exclude specific values, use the NOT IN clause: SELECT * FROM table WHERE MOD(column_name, 2) = 0 AND column_name NOT IN (excluded_value1, excluded_value2);

• You can also use a subquery to exclude values: SELECT * FROM table WHERE MOD(column_name, 2) = 0 AND column_name NOT IN (SELECT excluded_column ...read more