Oracle Plsql Developer Interview Questions and Answers

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

Explanation of triggers and their types in PL/SQL

• Triggers are database objects that are automatically executed in response to certain events

• Types of triggers include DML, DDL, and system triggers

• Syntax for creating a trigger: CREATE [OR REPLACE] TRIGGER trigger_name {BEFORE|AFTER} {INSERT|UPDATE|DELETE} ON table_name [FOR EACH ROW] [WHEN condition] BEGIN ... END;

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 ...read more

Temp table is a table created temporarily in memory. Temp variable is a variable that holds temporary data.

• Temp table is used to store data temporarily during a session

• Temp variable is used to hold temporary data that is not needed after a certain point

• Temp table and variable are created using the 'CREATE GLOBAL TEMPORARY' and 'DECLARE' statements respectively

• Example: CREATE GLOBAL TEMPORARY TABLE temp_table (id NUMBER...read more

A mutating table or mutating trigger occurs when a trigger tries to update a table that is currently being modified.

• Mutating table occurs when a trigger references the table that is being modified.

• It can happen when a trigger is fired by an INSERT, UPDATE, or DELETE statement on the table.

• This can lead to unpredictable results or errors, such as ORA-04091: table is mutating, trigger/function may not see it.

• To avoid mut...read more

Autonomous transaction is a separate transaction initiated by a parent transaction.

• It allows a subtransaction to commit or rollback independently of the parent transaction.

• It is useful for logging or auditing purposes.

• It can be created using the PRAGMA AUTONOMOUS_TRANSACTION statement.

• Example: A parent transaction updates a table, while an autonomous transaction logs the changes made.

• Example: An autonomous transaction ...read more

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 compar...read more

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 updat...read more

Truncate removes all data, delete removes selected data.

• Truncate is faster than delete as it doesn't log individual row deletions.

• Truncate cannot be rolled back, delete can be.

• Truncate resets identity columns, delete doesn't.

• Truncate doesn't fire triggers, delete does.

• Truncate is a DDL operation, delete is a DML operation.

A procedure in PL/SQL is a named block of code that can be called and executed multiple times.

• Syntax: CREATE [OR REPLACE] PROCEDURE procedure_name [(parameter1 [mode1] datatype1 [, parameter2 [mode2] datatype2]...)] IS

• Difference between procedure and function: Procedures do not return a value, while functions return a value.

• Procedures are used to perform an action, while functions are used to calculate and return a val...read more

To find if two tables have similar data, compare the records in both tables using a join or a subquery.

• Use a join operation to compare the records in both tables based on a common column.

• If the tables have a primary key, you can join them on that key to check for similar data.

• Alternatively, you can use a subquery to compare the data in both tables and check for matching records.

• Consider using the MINUS operator to find...read more

HAVING is used to filter groups while GROUP BY is used to group rows based on a column.

• HAVING is used with GROUP BY to filter groups based on a condition

• GROUP BY is used to group rows based on a column

• HAVING is used after GROUP BY in a query

• GROUP BY is used before HAVING in a query

• Example: SELECT department, AVG(salary) FROM employees GROUP BY department HAVING AVG(salary) > 5000;

A view is a virtual table created by a query. It does not store data itself but displays data from one or more tables. Views can be used for querying data as if it were a table.

• Views are created using a SELECT statement with optional joins, WHERE clauses, etc.

• Views can simplify complex queries by pre-defining joins and filters.

• Views do not store data themselves, they display data from underlying tables.

• Views can be upd...read more

A synonym is an alternative name for a table, view, sequence, or other database object.

• Synonyms can be used to provide a different name for an object, making it easier to reference.

• They can be created to reference objects in other schemas or databases.

• Synonyms can be public (accessible to all users) or private (accessible only to the creator).

A sequence is a database object in Oracle that generates unique numbers in a specified order.

• Used to generate unique numbers for primary key columns

• Can be used in INSERT statements to automatically generate values

• Can be defined to increment by a specific value and start at a specific number

Procedures are named PL/SQL blocks that perform a specific task. They can accept parameters and return values.

• Procedures are stored in the database and can be called by other PL/SQL blocks or applications.

• They can accept input parameters to perform operations and can also return output values.

• Procedures help in modularizing code and promoting reusability.

• Example: CREATE PROCEDURE calculate_salary (emp_id IN NUMBER) IS

Procedures do not return any value while functions return a value.

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

• Procedures do not have a return statement, while functions must have a return statement.

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

Partitions in PL/SQL are used to divide a table into smaller, more manageable pieces.

• Partitions help improve query performance by allowing data to be stored in separate segments based on a specified criteria.

• Common partitioning methods include range, hash, list, and composite partitioning.

• Example: Partitioning a sales table by month can improve query performance when searching for sales data within a specific time fram