40+ Senior Plsql Developer Interview Questions and Answers

Yes, I have worked on query tuning and optimization. Explain plan helps in identifying the execution plan of a query.

• I have experience in identifying and resolving performance issues in SQL queries.

• I use explain plan to analyze the query execution plan and identify any bottlenecks.

• I look for factors like full table scans, index usage, and join methods to optimize the query.

• I also use tools like SQL Trace and TKPROF to identify performance issues.

• For example, I optimized a que...read more

Use an anonymous PL/SQL block to check for column existence before adding it to a table.

• Use a SELECT statement on USER_TAB_COLUMNS to check if the column exists.

• If the column exists, raise a user-friendly exception.

• If it doesn't exist, use EXECUTE IMMEDIATE to add the column.

A package is a collection of related functions, procedures, and other program objects.

• Syntax: CREATE [OR REPLACE] PACKAGE package_name AS

• Package can contain variables, constants, cursors, exceptions, types, subprograms.

• Syntax: CREATE [OR REPLACE] PACKAGE BODY package_name AS

• Package body contains the implementation of the subprograms declared in the package specification.

PK is Primary Key and UK is Unique Key. PK does not allow nulls while UK allows only one null value.

• PK is used to uniquely identify each record in a table, while UK ensures that all values in a column are unique.

• PK does not allow duplicate values, while UK allows duplicate values except for one null value.

• Example: If a table has a PK on column 'ID', each record must have a unique ID value. If a table has a UK on column 'Email', all email values must be unique except for one n...read more

Inner join returns matching rows, left join returns all from left, right join returns all from right table.

• Inner Join: Combines rows from both tables where there is a match. Example: SELECT * FROM A INNER JOIN B ON A.id = B.id;

• Left Join: Returns all rows from the left table and matched rows from the right. Example: SELECT * FROM A LEFT JOIN B ON A.id = B.id;

• Right Join: Returns all rows from the right table and matched rows from the left. Example: SELECT * FROM A RIGHT JOIN B ...read more

The code block generates a sequence of numbers increasing by 3, starting from 1, up to 99.

• Use a loop to iterate through numbers from 1 to 99.

• Increment the number by 3 in each iteration.

• Print the number if it is less than or equal to 99.

Cursors in PL/SQL manage query results; SYS_REFCURSOR allows dynamic result sets in procedures and functions.

• Cursors are pointers to context areas for SQL statements.

• Types of cursors: Explicit (defined by the programmer) and Implicit (automatically created by Oracle).

• SYS_REFCURSOR is a predefined cursor type that can hold a result set dynamically.

• Syntax for declaring SYS_REFCURSOR: 'TYPE ref_cursor IS REF CURSOR;'.

• Example of using SYS_REFCURSOR in a stored procedure: 'PROCEDU...read more

Use the TRUNC function to get the first day of the current month in SQL.

• Use the TRUNC function: `SELECT TRUNC(SYSDATE, 'MM') FROM dual;`

• SYSDATE returns the current date and time.

• TRUNC with 'MM' truncates the date to the first day of the month.

• This query works in Oracle SQL.

An explain plan provides details on how a SQL query will be executed, including the execution path and resource usage.

• Execution Order: Shows the sequence in which operations are performed, e.g., SELECT, JOIN, FILTER.

• Access Methods: Indicates how data is accessed, such as full table scans or index scans.

• Join Methods: Describes how tables are joined, e.g., nested loops, hash joins.

• Cost Estimates: Provides estimated resource usage, including CPU and I/O costs.

• Cardinality Estimat...read more

Pragma autonomous transactions allow a PL/SQL subprogram to commit or rollback its own transactions independently of its caller.

• Pragma autonomous transactions are used to execute a transaction independently of the main transaction.

• It allows a subprogram to commit or rollback its own transactions without affecting the main transaction.

• Autonomous transactions are often used for logging, auditing, or error handling purposes.

• To declare an autonomous transaction, use the PRAGMA AU...read more

An insert/update statement in Oracle database is parsed by the SQL parser to check syntax and semantics.

• The SQL parser first checks the syntax of the insert/update statement to ensure it follows the rules of the SQL language.

• Next, the parser checks the semantics of the statement, which involves verifying the existence and accessibility of the tables and columns referenced in the statement.

• During parsing, the parser also determines the execution plan for the statement, which i...read more

Partitions are useful for managing large tables and improving query performance.

• Partitions allow for data to be split into smaller, more manageable chunks

• Queries can be run on specific partitions, improving performance

• Partitions can be based on various criteria such as date, range, or hash

• Example: Partitioning a sales table by date can improve query performance for recent sales data

• Example: Partitioning a customer table by region can improve query performance for regional ana...read more

Hints in PL/SQL guide the optimizer to improve query performance by influencing execution plans.

• Hints are special comments in SQL statements that provide instructions to the optimizer.

• Examples include 'USE_NL' to enforce a nested loop join or 'INDEX' to force the use of a specific index.

• They can help in scenarios where the optimizer's default choices lead to suboptimal performance.

• Hints can be used to control join methods, access paths, and even parallel execution.

• Syntax for ...read more

Indexes are database structures that improve query performance by allowing faster data retrieval.

• Indexes are like a book's index, helping locate data quickly without scanning the entire table.

• They are stored in a separate structure, often as B-trees or hash tables, which organize data for efficient access.

• For example, a B-tree index allows for logarithmic time complexity for search operations.

• Indexes can be unique (ensuring no duplicate values) or non-unique (allowing duplica...read more

Hard parse is when SQL statement is parsed every time it is executed. Soft parse is when SQL statement is parsed only once.

• Hard parse is resource-intensive and can slow down performance.

• Soft parse is faster and more efficient.

• Hard parse occurs when there is a syntax error or when the SQL statement is not in the shared pool.

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

• Hard parse can be avoided by using bind variables.

• Soft parse can be affected by chan...read more

Triggers in PL/SQL automate actions in the database, while audit tables track changes for compliance and data integrity.

• Types of Triggers: There are three main types of triggers - BEFORE, AFTER, and INSTEAD OF, which determine when the trigger action occurs.

• Example of a BEFORE Trigger: A trigger that validates data before an insert operation, ensuring no null values are entered.

• Audit Tables: These are special tables designed to log changes made to other tables, capturing deta...read more

To access elements in XML/JSON data, use appropriate methods like XPath for XML and dot notation for JSON.

• For XML data, use XPath expressions to navigate and extract specific elements or attributes.

• For JSON data, use dot notation to access nested objects or arrays.

• In PL/SQL, you can use XMLTable or JSON_TABLE functions to extract data from XML or JSON respectively.

Materialized views store query results for faster access, improving performance in data retrieval and reporting.

• Materialized views are precomputed query results stored on disk, reducing the need for complex joins during runtime.

• They are useful in data warehousing for summarizing large datasets, e.g., sales data aggregated by month.

• Materialized views can be refreshed periodically or on-demand, ensuring data is up-to-date without impacting performance.

• They can improve performan...read more

DELETE removes specific rows, TRUNCATE removes all rows quickly, and DROP deletes the entire table structure.

• DELETE: Removes specific rows based on a condition. Example: DELETE FROM employees WHERE id = 1;

• TRUNCATE: Removes all rows from a table but keeps the structure. Example: TRUNCATE TABLE employees;

• DROP: Deletes the entire table and its structure from the database. Example: DROP TABLE employees;

• DELETE is slower as it logs each row deletion, while TRUNCATE is faster as it ...read more

Use SQL query to find employees who were absent for 2 consecutive days.

• Use a SQL query to join the employee table with the attendance table

• Filter the results to only include employees who have consecutive absent days

• Group the results by employee to identify those who were absent for 2 consecutive days

Varrays are fixed-size arrays while Nested Tables are dynamic arrays in PL/SQL.

• Varrays have a maximum size specified at declaration, while Nested Tables can grow dynamically.

• Varrays are stored in contiguous memory locations, while Nested Tables are stored in a separate table.

• Varrays can be sparse, while Nested Tables are always dense.

• Example: Varray - DECLARE TYPE phone_numbers IS VARRAY(3) OF VARCHAR2(15); Nested Table - DECLARE TYPE phone_numbers IS TABLE OF VARCHAR2(15);

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

• Indexes are used to quickly locate data without having to search every row in a table.

• Types of indexes include B-tree indexes, bitmap indexes, and function-based indexes.

• Examples of indexes are primary keys, unique constraints, and indexes created explicitly on columns.

As a Senior PL/SQL Developer, I have extensive experience in database design, optimization, and complex query development.

• Database Design: Designed and implemented normalized database schemas for various applications, ensuring data integrity and efficiency.

• Performance Tuning: Optimized PL/SQL code and SQL queries, reducing execution time by up to 50% through indexing and query restructuring.

• Stored Procedures and Functions: Developed reusable stored procedures and functions fo...read more

No, COMMIT cannot be used in triggers.

• COMMIT cannot be used in triggers as it can cause mutating table errors.

• Triggers are automatically committed by the database after they are executed.

• Using COMMIT in triggers can lead to data integrity issues and performance problems.

Union combines and removes duplicates, Union All combines without removing duplicates.

• Union combines result sets and removes duplicates

• Union All combines result sets without removing duplicates

• Union is slower than Union All as it involves removing duplicates

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

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

Hierarchical data can be fetched using recursive queries or hierarchical queries.

• Recursive queries use a common table expression (CTE) to repeatedly join a table to itself.

• Hierarchical queries use the CONNECT BY clause to specify the parent-child relationship.

• Both methods require a column that identifies the parent of each row, such as an ID or parent ID column.

• Example: SELECT * FROM employees WHERE manager_id = 123 CONNECT BY PRIOR employee_id = manager_id

• Example: WITH recur...read more

A materialized view is a database object that contains the results of a query and is stored on disk for faster access.

• Materialized views store the results of a query like a table, allowing for faster access to data.

• They are updated periodically to reflect changes in the underlying data.

• Materialized views are commonly used in data warehousing and reporting applications.

• Example: CREATE MATERIALIZED VIEW mv_sales AS SELECT product_id, SUM(amount) FROM sales GROUP BY product_id;