Oracle Coding Concepts: SELECT Statement

**Understanding Oracle SELECT Statement: Real-Time Examples**

In the world of relational databases, the SELECT statement stands as a cornerstone, offering a powerful means to retrieve and manipulate data. Oracle, a leading database management system, utilizes the SELECT statement extensively.

Let's delve into its workings with some real-time examples to grasp its versatility and importance.

### Basic SELECT Statement:-- The simplest form of a SELECT statement retrieves all columns from a table.





SELECT * FROM employees;


Here, `employees` is a table containing details of all employees. The asterisk (*) denotes all columns.


### Selecting Specific Columns If you're interested in specific columns, say `employee_id` and `first_name`, you'd modify the statement as:





SELECT employee_id, first_name FROM employees;


### Filtering with WHERE Clause Often, you need to filter results based on certain conditions. For instance, if you want to retrieve details of employees with a salary above 5000:





SELECT * FROM employees WHERE salary > 5000;


### Ordering Results The ORDER BY clause allows sorting results. To sort employees by salary in descending order:





SELECT * FROM employees ORDER BY salary DESC;


### Limiting Results In cases where you want to fetch a limited number of rows, you can use the FETCH FIRST clause:





SELECT * FROM employees FETCH FIRST 10 ROWS ONLY;


### Joining Tables Joining tables enables retrieval of data from multiple tables. Suppose we have an `employees` table and a `departments` table. To fetch employees with their respective departments:





SELECT e.first_name, d.department_name


FROM employees e


JOIN departments d ON e.department_id = d.department_id;


### Real-time Example: Sales Analysis Imagine you're analyzing sales data from two tables: `orders` and `customers`.


- `orders` table has columns: order_id, customer_id, order_date, and amount.


- `customers` table has columns: customer_id, customer_name, and region.


To find total sales amount from each region for the last month:





SELECT c.region, SUM(o.amount) as total_sales


FROM orders o


JOIN customers c ON o.customer_id = c.customer_id


WHERE o.order_date >= SYSDATE - 30


GROUP BY c.region;


This statement adds {orders} and `customers} together based on {customer_id}, removes orders older than 30 days, aggregates results by region, and totalizes sales. You can learn how to interface with the Oracle database using SQL in the Oracle basics section. You will discover how to create tables, change the values of columns, and remove rows from tables that have conditions or don't have conditions, as well as numerous methods for querying data from the SQL Developer database.





In Oracle, tables are consists of columns and rows. For example, the customers table in the sample database has the following columns: customer_id, name, address, website and credit_limit. The customers table also has some meaningfull values in these columns that we will use to manipulate the oracle database.


customers table To retrieve data from one or more columns of a table, you use the SELECT statement with the following syntax:


SELECT column_1, column_2, ... FROM table_name;


Statement selected:


The table name from which you wish to query the data must first be specified.


Next, specify the columns you wish the data to be returned from. A comma (,) must be used to separate each column if you have more than one.


Keep in mind that the SELECT statement is quite intricate and includes numerous clauses, including ORDER BY, GROUP BY, HAVING, and JOIN. To keep things easy, throughout this guide,


Only the SELECT and FROM clauses are being discussed.


Let's examine a few examples to gain a better understanding of how the Oracle SELECT statement operates.


A) query information from just one column


Use the following statement to retrieve the client names from the customers table:


CHOOSE name FROM the clientele;


B) Conducting a multi-column query


You provide a list of comma-separated column names in order to query data from multiple columns.


The customer table's customer_id, name, and credit_limit columns can be queried using the example below.


SELECT name, credit limit, and customer id FROM customers;


C) Querying a table's entire set of columns for data


you can use the shorthand asterisk (*) to instruct Oracle to return data from all columns of a table as follows: SELECT * FROM customers;


Important Notes: To know more about Oracle Queries, Please go through the below youtube video links:-----------

Topics that are covered in Videos: Visit Oracle Database tutorial


Oracle SQL Query Part 1


Oracle SQL Query part 2


Oracle Dual table and Alias Column


Oracle fetch clause, Oracle in and not in operator


Oracle between, Oracle Like Operator


Oracle IS NULL operator, , Oracle Joins (inner, left, right and full outer join)


Oracle Cross Join, Oracle self join


Oracle UNION, Oracle intersect, Oracle minus


Oracle Subquery, Oracle corelated subquery with exists operator


Oracle exists update stmt, ,Oracle Any operator


Oracle All operator, view creation, Oracle Rollup


Oracle PIVOT clause, Oracle UNPIVOT


Oracle INSERT , Oracle INSERT INTO SELECT


Oracle Update, Oracle Delete


Oracle MERGE statement


UnConditional Oracle INSERT ALL statement, Conditional Oracle INSERT ALL statement


Oracle CASE Expression


### Conclusion The Oracle SELECT statement offers a robust and flexible mechanism to retrieve, filter, and manipulate data. Whether it's fetching specific columns, applying conditions with WHERE, or joining tables for complex analysis, its versatility is unmatched. By understanding these concepts and practicing with real-time examples, you can harness the full potential of Oracle's SELECT statement in your database operations.