100+ Plsql Developer Interview Questions and Answers

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 value.

• Procedures can have OUT or IN OUT parameters to pass va...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, name VARCHAR2(50));

• Example: DECLARE temp_var VARCHAR2(50...read more

PL/SQL program to print numbers in descending order from 103 to 3

• Use a loop to iterate from 103 to 3

• Print each number in the loop

• Decrement the loop counter by 3 in each iteration

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 mutating table errors, use row-level triggers instead of stat...read more

SQL query to delete duplicate records from a table.

• Use the DELETE statement with a subquery to identify and delete duplicate records.

• The subquery should select the duplicate records based on the criteria for duplication.

• Ensure to keep at least one copy of the duplicate records to avoid deleting all instances.

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 sends an email notification after a parent transaction com...read more

To eliminate duplicates without using the distinct command in PL/SQL, we can use the GROUP BY clause.

• Use the GROUP BY clause to group the data by the columns that you want to eliminate duplicates from.

• Select the columns you want to display in the result set.

• Aggregate functions like COUNT, SUM, AVG, etc. can be used to perform calculations on the grouped data.

• The GROUP BY clause ensures that only unique combinations of the grouped columns are returned.

The interview questions cover topics such as Oracle instance recovery, file systems, SQL/PL/SQL queries, Unix commands, and ITIL concepts.

• An instance in Oracle refers to the memory structures and background processes that manage a database.

• Instance recovery is the process of bringing a database instance back to a consistent state after a failure.

• Oracle has both logical and physical file systems. The logical file system includes tablespaces, data files, and control files, whil...read more

Joins are used to combine rows from two or more tables based on related columns. There are different types of joins.

• Types of joins: inner join, left join, right join, full outer join, cross join

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

• Natural join is a type of join that automatically matches columns with the same name in both tables

• Example: SELECT * FROM employees NATURAL JOIN departments;

Global temp table is a temporary table that can be accessed by multiple sessions.

• Global temp table is created using CREATE GLOBAL TEMPORARY TABLE statement.

• Data in global temp table is visible to all sessions but is deleted when the session that created it ends.

• Global temp table can be used to store intermediate results in a multi-step process.

• In my project, I used global temp table to store data temporarily while performing complex calculations.

Soft parsing is reusing the existing execution plan while hard parsing is generating a new execution plan.

• Soft parsing is faster as it avoids the overhead of generating a new execution plan.

• Hard parsing is slower as it involves generating a new execution plan.

• Soft parsing occurs when the SQL statement is already in the shared pool.

• Hard parsing occurs when the SQL statement is not in the shared pool or needs a new execution plan.

• Soft parsing saves CPU and memory resources.

• Hard...read more

Procedure to create dummy tables of whole schema

• Loop through all tables in schema

• Create a new table with same structure and name as original table

• Insert dummy data into new table

Implicit cursors are automatically created by the Oracle server, while explicit cursors are explicitly declared by the programmer.

• Implicit cursors are used for single-row queries, while explicit cursors are used for multi-row queries.

• Implicit cursors are automatically opened, fetched, and closed by the Oracle server, while explicit cursors need to be manually opened, fetched, and closed by the programmer.

• Implicit cursors are less flexible and have limited control, while expli...read more

Indexing is a technique used in databases to improve the performance of queries by creating a data structure that allows for faster data retrieval.

• Indexing creates a separate data structure that contains a subset of the data in the database, organized in a way that allows for efficient searching and retrieval.

• Indexes are created on one or more columns of a table and can be used to quickly locate data based on the values in those columns.

• By using indexes, database systems can ...read more

A view is a virtual table created from one or more tables. It can be used to simplify complex queries and provide a customized view of data.

• A view is a stored query that can be treated as a table

• Types of views include simple views, complex views, and materialized views

• A complex view is a view that involves multiple tables or subqueries

• Complex views can be used to combine data from different tables or apply complex calculations

• Example of a complex view: CREATE VIEW employee_de...read more

Case and decode are conditional expressions in PL/SQL used for data manipulation.

• CASE is used for conditional logic in SQL statements, while DECODE is used for conditional logic in SELECT statements.

• CASE is more flexible and can handle multiple conditions, while DECODE is limited to one condition.

• CASE can be used in both SQL and PL/SQL, while DECODE is specific to SQL.

• Example of CASE: SELECT CASE WHEN condition1 THEN result1 WHEN condition2 THEN result2 ELSE default_result EN...read more

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

• A package consists of two parts: package specification and package body.

• The package specification defines the public interface of the package, including declarations of variables, constants, cursors, procedures, and functions.

• The package body contains the actual implementation of the procedures and functions declared in the package specification.

• It is not possible to use a pa...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;

To copy the structure of a table without copying the data, you can use the CREATE TABLE AS SELECT statement.

• Use the CREATE TABLE AS SELECT statement to create a new table with the same structure as the original table.

• Specify the columns and their data types in the SELECT statement, but exclude the actual data from the original table.

• Example: CREATE TABLE new_table AS SELECT * FROM original_table WHERE 1=0;

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 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

Yes, I have performed performance tuning by identifying bottlenecks and optimizing queries.

• Identified slow queries using tools like SQL Trace, Explain Plan, and AWR reports.

• Optimized queries by adding indexes, rewriting SQL statements, and reducing unnecessary data retrieval.

• Tuned PL/SQL code by using bulk processing, minimizing context switches, and optimizing loops.

• Utilized database features like partitioning and materialized views for performance improvement.

No, it is not possible to combine two tables with differing data and columns without utilizing joins.

• Joins are necessary to combine tables based on a common column or key.

• Different data and columns require a join to match and merge the data properly.

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

No, a package body cannot be used without a package specification.

• A package body must always be associated with a package specification.

• The package specification defines the public interface of the package, while the package body contains the implementation details.

• Attempting to use a package body without a corresponding package specification will result in compilation errors.

Rank assigns unique ranks to each distinct row, while Dense Rank assigns consecutive ranks without gaps.

• Rank may have gaps in the ranking sequence, while Dense Rank does not.

• Rank assigns the same rank to rows with the same values, while Dense Rank assigns different ranks.

• Rank function is non-consecutive, while Dense Rank function is consecutive.

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;

Char is fixed length, varchar is variable length with max 4000 bytes, varchar2 is variable length with max 32767 bytes.

• Char is fixed length and always right-padded with spaces, while varchar and varchar2 are variable length.

• Varchar can store up to 4000 bytes of data, while varchar2 can store up to 32767 bytes.

• Char is less efficient in terms of storage compared to varchar and varchar2.

Writing a SQL query with a subquery involves nesting one query inside another to retrieve specific data.

• Start by writing the main query that will retrieve the primary data

• Identify the criteria for the subquery to filter the results

• Enclose the subquery within parentheses and use it in the WHERE or FROM clause of the main query

• Ensure that the subquery returns a single value or a single column result

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.

Indexes are database structures used to improve query performance.

• Indexes are created on one or more columns of a table.

• They allow for faster data retrieval by reducing the number of disk I/O operations.

• However, they can slow down data modification operations such as INSERT, UPDATE, and DELETE.

• Indexes can also take up significant disk space and memory.

• Different types of indexes include B-tree, bitmap, and hash indexes.

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

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

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.

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

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 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

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

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

Using GROUP BY clause with aggregate functions can obtain distinct values without using the DISTINCT keyword.

• Use GROUP BY clause with aggregate functions like COUNT, SUM, AVG, etc.

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

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.

Indexes should be created on columns that are frequently used in WHERE, JOIN, and ORDER BY clauses.

• Indexes should be created on columns with high selectivity

• Indexes should not be created on columns with low cardinality

• Indexes should not be created on columns with frequent updates

• Composite indexes can be created on multiple columns

• Indexes can be created on virtual columns

VARCHAR can store up to 2000 bytes while VARCHAR2 can store up to 4000 bytes.

• VARCHAR can store variable-length character strings up to 2000 bytes.

• VARCHAR2 can store variable-length character strings up to 4000 bytes.

• VARCHAR will occupy space for NULL values while VARCHAR2 will not.

• VARCHAR2 is more efficient in terms of storage and performance compared to VARCHAR.

Explanation of SQL Loader, Procedure, Package, Function, Bulk Collect, Cursor

• SQL Loader is a tool used to load data from external files into Oracle database tables

• Procedure is a named block of PL/SQL code that performs a specific task

• Package is a collection of related procedures, functions, variables, and cursors

• Function is a named block of PL/SQL code that returns a value

• Bulk Collect is a method used to fetch multiple rows of data from a query into a collection

• Cursor is a po...read more

GTT stands for Global Temporary Table, which is a temporary table used to store data temporarily during a session.

• GTT is a temporary table that is created and used within a session

• Data in GTT is visible only to the session that created it

• GTT is automatically dropped at the end of the session or when the transaction is committed or rolled back