30+ Oracle SQL and PLSQL Developer Interview Questions and Answers

Analytical functions are used to perform calculations across a set of rows related to the current row.

• Analytical functions are used to calculate aggregate values based on a group of rows.

• They can be used to calculate running totals, moving averages, rank, percentiles, etc.

• Examples include functions like ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD(), SUM() OVER(), AVG() OVER().

Context switching is the process of storing and restoring the state of a CPU so that multiple processes can share the same CPU.

• Context switching allows the CPU to switch from one process to another, enabling multitasking.

• In Oracle PLSQL, collection types are used to store multiple values in a single variable.

• Examples of collection types in PLSQL include arrays, nested tables, and associative arrays.

Set operators are used to combine the result sets of two or more SELECT statements. UNION ALL keeps duplicates.

• Set operators include UNION, UNION ALL, INTERSECT, and MINUS

• UNION ALL retains duplicate rows from the result sets

• Example: SELECT column1 FROM table1 UNION ALL SELECT column1 FROM table2

Without commit in pragma procedure, changes will not be permanently saved in the database.

• Changes made in the procedure will not be saved to the database permanently.

• Other sessions will not be able to see the changes until a commit is issued.

• Rollback will discard any changes made in the procedure without commit.

Use Oracle External Tables and SQL Loader to process files in different formats and from different sources to load a single table.

• Create External Tables in Oracle to define the structure of the files from different sources.

• Use SQL Loader to load data from the files into the External Tables.

• Transform and manipulate the data as needed using SQL queries before inserting into the final table.

Yes, it is possible to perform DML (Data Manipulation Language) operations on a view in Oracle SQL.

• DML operations such as INSERT, UPDATE, and DELETE can be performed on a view in Oracle SQL.

• The view must be updatable, meaning it must meet certain criteria such as having a key-preserved table in the FROM clause.

• Changes made to the view will affect the underlying base tables.

• For example, you can insert data into a view that is based on multiple tables, and the data will be inse...read more

Joining tables is done using JOIN keyword. Types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

• JOIN keyword is used to combine rows from two or more tables based on a related column between them.

• INNER JOIN returns only the matching rows from both tables.

• LEFT JOIN returns all rows from the left table and the matching rows from the right table.

• RIGHT JOIN returns all rows from the right table and the matching rows from the left table.

• FULL JOIN returns all row...read more

Common null handling functions in Oracle SQL and PLSQL.

• NVL function replaces null values with a specified default value.

• NVL2 function returns one value if a specified expression is not null, otherwise returns another value.

• NULLIF function returns null if two expressions are equal, otherwise returns the first expression.

• COALESCE function returns the first non-null expression in a list of expressions.

Collections are data structures used to store multiple values of the same data type.

• Types of collections in Oracle are Associative arrays, Nested tables, and Varrays.

• Associative arrays are indexed by string values, Nested tables are like arrays with no fixed size, and Varrays are like arrays with a fixed size.

• Collections can be used to pass multiple values to a stored procedure or function.

The log file structure in concurrent program

• The log file is a text file that contains information about the execution of a concurrent program

• It includes details like start and end time, parameters passed, and any errors encountered

• The log file is stored in the $APPLCSF/$APPLLOG directory on the application server

• The file name follows a specific naming convention: _.log

Answers to common questions in Oracle SQL and PLSQL Developer interview.

• Data is a collection of facts, figures, and statistics that can be processed to derive information.

• A database is a structured collection of data that is stored and organized in a way that allows for efficient retrieval and manipulation.

• Delete removes specific rows from a table while truncate removes all rows from a table.

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

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

• Inner join returns only the rows that have matching values in both tables

• Left join returns all the rows from the left table and the matched rows from the right table

• Inner join is more restrictive as it requires a match in both tables, while left join is less restrictive

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

• Example: SELECT * FROM table1 LEFT JOIN tabl...read more

Use CONNECT BY LEVEL to print numbers from 1 to 10 in Oracle SQL

• Use CONNECT BY LEVEL to generate rows from 1 to 10

• Select the generated numbers in the query

Record is a composite data type that stores related fields together.

• A record is a user-defined data type that contains a group of related data items.

• It is also known as a row or tuple in a table.

• Each field in a record can have a different data type.

• Records are commonly used in PL/SQL to hold query results or to pass data between procedures.

• Example: DECLARE emp_rec employees%ROWTYPE;

• This creates a record variable emp_rec that contains all the columns of the employees table.

Reference cursor in procedure is used to return result sets from a stored procedure.

• Declare a cursor variable in the procedure using TYPE keyword

• Open the cursor variable using OPEN keyword

• Fetch data from the cursor using FETCH keyword

• Close the cursor using CLOSE keyword after fetching all data

Cannot answer without more context. Need to know what 'cp' refers to.

• Need more information about what 'cp' is referring to in order to provide a full code explanation.

• Without context, it is impossible to provide a meaningful answer.

• Please provide more information about the specific code or program in question.

Merge statement is used to perform insert, update, or delete operations in a single statement based on a condition.

• Combines INSERT, UPDATE, and DELETE operations into a single statement

• Used to synchronize two tables based on a condition

• Improves performance by reducing the number of SQL statements needed

• Can be used to insert new records, update existing records, or delete records in a single operation

SQL is the language used for managing and manipulating databases.

• SQL stands for Structured Query Language

• It is used to communicate with databases to perform tasks like querying data, updating records, and creating tables

• Examples of SQL commands include SELECT, INSERT, UPDATE, and DELETE

Set operators are used to combine the result sets of two or more SELECT statements.

• Set operators include UNION, UNION ALL, INTERSECT, and MINUS.

• UNION combines the result sets of two SELECT statements, removing duplicates.

• UNION ALL combines the result sets of two SELECT statements, including duplicates.

• INTERSECT returns only the rows that appear in both result sets.

• MINUS returns only the rows that appear in the first result set but not in the second.

OLAP systems are designed for analyzing and managing large volumes of data from multiple perspectives.

• OLAP stands for Online Analytical Processing

• OLAP systems allow users to analyze data in real-time

• They provide advanced analytics capabilities like data mining, forecasting, and trend analysis

• Examples of OLAP systems include Oracle Essbase, Microsoft Analysis Services, and IBM Cognos

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

• Primary key ensures data integrity by preventing duplicate rows.

• Primary key can be a single column or a combination of columns.

• Primary key is used as a reference in foreign keys of other tables.

• Primary key values cannot be null.

• Primary key values must be unique.

No, you cannot commit in a trigger as it can cause mutating table errors.

• Triggers cannot contain COMMIT or ROLLBACK statements.

• Committing in a trigger can lead to mutating table errors.

• Instead, use triggers for data validation, not for committing transactions.

Yes, you can update in a function in Oracle SQL and PLSQL.

• You can use the UPDATE statement within a PLSQL function to update data in a table.

• Make sure to commit the changes using COMMIT statement.

• Example: CREATE OR REPLACE FUNCTION update_employee_salary(emp_id IN NUMBER, new_salary IN NUMBER) RETURN NUMBER IS BEGIN UPDATE employees SET salary = new_salary WHERE employee_id = emp_id; COMMIT; RETURN 1; END;

Autonomous transaction is a separate transaction that is independent of the main transaction.

• Autonomous transactions are used to perform certain tasks independently of the main transaction.

• They are useful for logging, auditing, or error handling purposes.

• Autonomous transactions are started with the PRAGMA AUTONOMOUS_TRANSACTION statement.

• Changes made in an autonomous transaction are not visible to the main transaction until they are committed.

• Example: Creating a logging proce...read more

To create a table using another table, use the CREATE TABLE AS SELECT statement.

• Use the CREATE TABLE AS SELECT statement to create a new table based on the structure and data of an existing table.

• Specify the new table name after CREATE TABLE and the existing table name after AS SELECT.

• You can also add conditions or filters to the SELECT statement to customize the data being copied.

• Example: CREATE TABLE new_table AS SELECT * FROM existing_table WHERE condition;

Truncate is a DDL command that removes all rows from a table, while delete is a DML command that removes specific rows.

• Truncate is faster than delete as it does not generate undo logs.

• Truncate resets the high water mark of the table, while delete does not.

• Truncate cannot be rolled back, while delete can be rolled back using a transaction.

• Truncate does not fire any triggers, while delete does.

• Truncate does not require a WHERE clause, while delete does.

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

• Procedures do not return values, but can have output parameters

• Functions must return a value and cannot have output parameters

• Procedures can modify data, while functions cannot

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

Use a DELETE statement with a subquery to remove duplicates in a table.

• Identify the columns that define duplicates

• Use a subquery to select the rows to be deleted

• Use the DELETE statement to remove the duplicates

An index is a database object that improves the speed of data retrieval operations on a table.

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

• Syntax to create an index: CREATE INDEX index_name ON table_name(column_name);

• Indexes can be unique or non-unique.

• Indexes can be used to enforce uniqueness constraints.

• Indexes can improve query performance by reducing the number of rows that need to be scanned.

Use SQL query with MAX function to fetch highest salary from the database.

• Use SELECT statement with MAX function to retrieve highest salary

• Specify the column name for salary in the SELECT statement

• Include the table name in the query if needed

Lead and lag functions are used to access data from a subsequent or previous row in a result set.

• Lead function is used to access data from the next row in the result set.

• Lag function is used to access data from the previous row in the result set.

• Both functions can be used to compare values between rows or calculate differences.

The question is asking to identify different types of joins in SQL.

• Inner Join: Returns rows when there is a match in both tables.

• Left Join: Returns all rows from the left table and the matched rows from the right table.

• Right Join: Returns all rows from the right table and the matched rows from the left table.

• Full Outer Join: Returns rows when there is a match in either table.

• Cross Join: Returns the Cartesian product of the two tables.

I would choose a location with a peaceful environment and good work-life balance.

• Prefer a location with low traffic and easy commute

• Look for nearby amenities like grocery stores, restaurants, and parks

• Consider the cost of living in the area

• Research the crime rate and safety of the neighborhood