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SQL SELECT Statement
Purpose:
The SELECT statement is used to select data from a database. The data returned is stored in a result table, sometimes called the result set.
Basic Syntax:
The basic syntax of the SELECT statement is: SELECT column1, column2, ... FROM table_name;
SELECT first_name, last_name FROM employees;
Example Explanation:
This example selects the first and last names of all employees from the "employees" table.
Console Output:
John Doe
Jane Smith
SQL WHERE Clause
Purpose:
The WHERE clause is used to filter records. It is used to extract only those records that fulfill a specified condition.
Basic Syntax:
The basic syntax of the WHERE clause is: SELECT column1, column2, ... FROM table_name WHERE condition;
SELECT * FROM employees WHERE department = 'Sales';
Example Explanation:
This example selects all columns from the "employees" table where the department is "Sales".
Console Output:
ID: 1, Name: John Doe, Department: Sales
SQL INSERT INTO Statement
Purpose:
The INSERT INTO statement is used to insert new records in a table.
Basic Syntax:
The basic syntax of the INSERT INTO statement is: INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);
INSERT INTO employees (first_name, last_name, department) VALUES ('Alice', 'Wonderland', 'HR');
Example Explanation:
This example inserts a new record into the "employees" table with the first name "Alice", last name "Wonderland", and department "HR".
Console Output:
Record inserted successfully.
SQL UPDATE Statement
Purpose:
The UPDATE statement is used to modify the existing records in a table.
Basic Syntax:
The basic syntax of the UPDATE statement is: UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition;
UPDATE employees SET department = 'Marketing' WHERE first_name = 'Alice';
Example Explanation:
This example updates the department of the employee with the first name "Alice" to "Marketing".
Console Output:
Record updated successfully.
SQL DELETE Statement
Purpose:
The DELETE statement is used to delete existing records in a table.
Basic Syntax:
The basic syntax of the DELETE statement is: DELETE FROM table_name WHERE condition;
DELETE FROM employees WHERE first_name = 'Alice';
Example Explanation:
This example deletes the record of the employee whose first name is "Alice".
Console Output:
Record deleted successfully.
SQL ORDER BY Clause
Purpose:
The ORDER BY keyword is used to sort the result set in ascending or descending order.
Basic Syntax:
The basic syntax of the ORDER BY clause is: SELECT column1, column2, ... FROM table_name ORDER BY column1, column2, ... ASC|DESC;
SELECT first_name, last_name FROM employees ORDER BY last_name DESC;
Example Explanation:
This example selects the first and last names of employees and sorts them by last name in descending order.
Console Output:
Smith, Jane
Doe, John
SQL GROUP BY Clause
Purpose:
The GROUP BY statement is used in conjunction with aggregate functions to group the result set by one or more columns.
Basic Syntax:
The basic syntax of the GROUP BY clause is: SELECT column1, aggregate_function(column2) FROM table_name GROUP BY column1;
SELECT department, COUNT(*) FROM employees GROUP BY department;
Example Explanation:
This example counts the number of employees in each department.
Console Output:
Sales: 5
HR: 3
SQL JOIN Clause
Purpose:
The JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Basic Syntax:
The basic syntax of the JOIN clause is: SELECT columns FROM table1 INNER JOIN table2 ON table1.column = table2.column;
SELECT employees.first_name, departments.department_name FROM employees INNER JOIN departments ON employees.department_id = departments.id;
Example Explanation:
This example selects the first names of employees along with their department names by joining the "employees" and "departments" tables.
Console Output:
John, Sales
Jane, HR
