Oracle SQL: Comprehensive Guide with Practical Code Examples

Introduction to Oracle SQL

Oracle SQL, or Structured Query Language, is a?powerful programming language designed for managing relational databases.?Oracle Corporation introduced Oracle SQL in the late 1970s as a part of their flagship product, the Oracle Database. Since then, Oracle SQL has become an industry?standard for managing and querying?relational databases.

Oracle SQL Features

Oracle SQL provides a wide range of features, including:

1. Robust data definition and manipulation capabilities
2. Advanced querying and reporting functionality
3. Support for complex transactions
4. Extensive built-in functions and operators
5. Integration with procedural languages like PL/SQL

Getting Started

Setting Up Environment

Before you can start working with Oracle SQL, you’ll need to have access to an?Oracle Database instance. You can either install Oracle Database on your local machine or use a cloud-based service like Oracle Cloud.

To install the Oracle Database on your local machine, you can download it from the?Oracle official website. Once your database is set up, you’ll need to connect to it using an Oracle SQL client, such as SQL*Plus, SQL Developer, or a third-party tool like DBeaver or Toad.

Basic Syntax

The basic syntax of an Oracle SQL statement consists of keywords, identifiers, literals, and operators.

Keywords are predefined words with special meaning in Oracle SQL, such as?SELECT,?INSERT, or?UPDATE. Identifiers are user-defined names for database objects like tables and columns. Literals represent constant values, and operators are symbols used to perform operations on data.

1. Data Definition Language (DDL)

1.1 CREATE TABLE Statement (DDL)

The?CREATE TABLE?statement is used to create a new table in the database. The syntax for creating a table is as follows:

CREATE TABLE table_name (
    column1_name datatype constraint,
    column2_name datatype constraint,
    ...
);        

Here’s an example of creating a simple?employees?table:

CREATE TABLE employees (
    id NUMBER PRIMARY KEY,
    first_name VARCHAR2(50),
    last_name VARCHAR2(50),
    salary NUMBER
);        

1.2 ALTER TABLE Statement (DDL)

The?ALTER TABLE?statement is used to modify an existing table, such as?adding,?modifying, or?dropping?columns. The syntax for altering a table is as follows:

ALTER TABLE table_name
    action column_name datatype constraint;        

For example, to?add a new column?called?department?to the?employees?table:

ALTER TABLE employees
    ADD department VARCHAR2(50);        

1.3 DROP TABLE Statement (DDL)

The?DROP TABLE?statement is used to?delete an existing table?and all its data. The syntax for dropping a table is as follows:

DROP TABLE table_name;        

For example, to delete the?employees?table:

DROP TABLE employees;        

2. Data Manipulation Language (DML)

2.1 INSERT INTO Statement (DML)

The?INSERT INTO?statement is used to rows into a table. The syntax for inserting data is as follows:

INSERT INTO table_name (column1, column2, ...)
VALUES (value1, value2, ...);        

For example, to?insert a new employee?into the?employees?table:

INSERT INTO employees (id, first_name, last_name, salary, department)
VALUES (1, 'John', 'Doe', 50000, 'IT');        

2.2 UPDATE Statement (DML)

The?UPDATE?statement is used to?modify existing rows?in a table. The syntax for updating data is as follows:

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;        

For example, to update the salary of an employee with?id?equal to 1:

UPDATE employees
SET salary = 55000
WHERE id = 1;        

2.3 DELETE Statement (DML)

The?DELETE?statement is used to remove rows from a table. The syntax for deleting data is as follows:

DELETE FROM table_name
WHERE condition;        

For example, to delete an employee with?id?equal to 1:

DELETE FROM employees
WHERE id = 1;        

3. Data Query Language (DQL)

3.1 SELECT Statement

The?SELECT?statement is used to?retrieve data?from one or more tables. The basic syntax for selecting data is as follows:

SELECT column1, column2, ...
FROM table_name
WHERE condition;        

For example, to retrieve all columns from the?employees?table:

SELECT * FROM employees;        

3.2 SELECT DISTINCT (DQL)

To retrieve unique values from a specific column, use the?SELECT DISTINCT?clause:

SELECT DISTINCT department FROM employees;        

3.3 WHERE and AND/OR (DQL)

The?WHERE?clause is used to?filter the data?returned by a?SELECT?statement. You can combine multiple conditions using the?AND?and?OR?operators:

SELECT * FROM employees
WHERE department = 'IT' AND salary > 50000;        

3.4 ORDER BY (DQL)

The?ORDER BY?clause is used to?sort the data?returned by a?SELECT?statement:

SELECT * FROM employees
ORDER BY last_name ASC, salary DESC;        

3.5 GROUP BY and HAVING

The?GROUP BY?clause is used to?group rows with the same values in specified columns. The?HAVING?clause is used to filter the results of a?GROUP BY:

SELECT department, COUNT(*) AS num_employees, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING COUNT(*) > 1
ORDER BY avg_salary DESC;        

Conclusion

In this article, we’ve covered the basics of Oracle SQL with code examples, including data definition language (DDL), data manipulation language (DML), and data query language (DQL).

By learning these fundamentals, you’ll be well-equipped to work with Oracle databases and create powerful, efficient queries.

FAQs

Q1: What is the difference between VARCHAR2 and VARCHAR in Oracle SQL?

A1: Both VARCHAR and VARCHAR2 are used to store variable-length character strings. However, Oracle recommends using VARCHAR2 instead of VARCHAR, as VARCHAR’s behavior might change in future releases, while VARCHAR2’s behavior is guaranteed to remain consistent.

How can I retrieve the top N rows in Oracle SQL?

To retrieve the top N rows, you can use the?FETCH FIRST N ROWS ONLY?clause:

SELECT * FROM employees
ORDER BY salary DESC
FETCH FIRST 10 ROWS ONLY;        

What is the difference between INNER JOIN and OUTER JOIN?

An INNER JOIN returns only the rows from both tables where there’s a match based on the specified condition.

An OUTER JOIN returns all rows from one table and the matching rows from the other table, filling in NULL values for non-matching rows.

How can I create an index in Oracle SQL?

To create an index, use the?CREATE INDEX?statement:

CREATE INDEX index_name
ON table_name (column_name);        

How can I create a view in Oracle SQL?

To create a view, use the?CREATE VIEW?statement:

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;        

Thank you for reading it,??. Credit Pandata