 Create table countries
CREATE TABLE countries (
    country_id INT PRIMARY KEY,
    country_name VARCHAR(50)
);

-- Insert some sample data into the countries table
INSERT INTO countries (country_id, country_name)
VALUES
    (1, 'United Kingdom'),
    (2, 'United States'),
    (3, 'France');

-- Create table locations
CREATE TABLE locations (
    location_id INT PRIMARY KEY,
    city VARCHAR(50),
    country_id INT,
    FOREIGN KEY (country_id) REFERENCES countries(country_id)
);

-- Insert some sample data into the locations table
INSERT INTO locations (location_id, city, country_id)
VALUES
    (1, 'London', 1),
    (2, 'New York', 2),
    (3, 'Paris', 3);

-- Create table department
CREATE TABLE department (
    department_id INT PRIMARY KEY,
    department_name VARCHAR(50),
    location_id INT,
    FOREIGN KEY (location_id) REFERENCES locations(location_id)
);

-- Insert some sample data into the department table
INSERT INTO department (department_id, department_name, location_id)
VALUES
    (1, 'Engineering', 1),
    (2, 'Marketing', 2),
    (3, 'Sales', 3);

-- Create table job
CREATE TABLE job (
    job_id INT PRIMARY KEY,
    job_title VARCHAR(50)
);

-- Insert some sample data into the job table
INSERT INTO job (job_id, job_title)
VALUES
    (1, 'Manager'),
    (2, 'Developer'),
    (3, 'Analyst'),
    (4, 'Designer');

-- Create table employee
CREATE TABLE employee (
    employee_number INT PRIMARY KEY,
    employee_name VARCHAR(50),
    job_title VARCHAR(50),
    salary DECIMAL(10, 2),
    department_id INT,
    FOREIGN KEY (department_id) REFERENCES department(department_id)
);

-- Insert some sample data into the employee table
INSERT INTO employee (employee_number, employee_name, job_title, salary, department_id)
VALUES
    (1, 'John Doe', 'Manager', 60000.00, 1),
    (2, 'Jane Smith', 'Developer', 50000.00, 1),
    (3, 'Michael Johnson', 'Analyst', 45000.00, 2),
    (4, 'Emily Brown', 'Designer', 55000.00, 2),
    (5, 'David Lee', 'Manager', 62000.00, 3),
    (6, 'Sarah Wilson', 'Developer', 51000.00, 3);

 SELECT e.employee_number, e.employee_name, e.job_title
FROM employee e
JOIN (
    SELECT department_id, AVG(salary) AS avg_salary
    FROM employee
    GROUP BY department_id
) AS dept_avg ON e.department_id = dept_avg.department_id
WHERE e.salary > dept_avg.avg_salary;

2. SELECT e.employee_number, e.employee_name, e.job_title
FROM employee e
JOIN department d ON e.department_id = d.department_id
JOIN locations l ON d.location_id = l.location_id
WHERE l.city = 'London';

3. SELECT e.employee_name
FROM employee e
JOIN (
    SELECT department_id, SUM(salary) AS total_salary
    FROM employee
    GROUP BY department_id
) AS dept_total ON e.department_id = dept_total.department_id
WHERE e.salary > 0.5 * dept_total.total_salary;

4. SELECT e.employee_name, e.salary, e.department_id
FROM employee e
JOIN (
    SELECT department_id, MIN(salary) AS min_salary
    FROM employee
    GROUP BY department_id
) AS dept_min ON e.department_id = dept_min.department_id
WHERE e.salary < dept_min.min_salary AND e.department_id = 70;

created 1 year ago by ranjeet purohit

MySQL online editor

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About MySQL

MySQL is a open-source, free and very popular relational database management system which is developed, distributed and supported by Oracle corporation.

Key Features:

Open-source relational database management systems.
Reliable, very fast and easy to use database server.
Works on client-server model.
Highly Secure and Scalable
High Performance
High productivity as it uses stored procedures, triggers, views to write a highly productive code.
Supports large databases efficiently.
Supports many operating systems like Linux*,CentOS*, Solaris*,Ubuntu*,Windows*, MacOS*,FreeBSD* and others.

Syntax help

Commands

1. CREATE

CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

Example

CREATE TABLE EMPLOYEE (
  empId INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  dept TEXT NOT NULL
);

2. ALTER

ALTER TABLE Table_name ADD column_name datatype;

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Dave', 'Sales');

3. TRUNCATE

TRUNCATE table table_name;

4. DROP

DROP TABLE table_name;

5. RENAME

RENAME TABLE table_name1 to new_table_name1;

6. COMMENT

Single-Line Comments:

 --Line1;

Multi-Line comments:

   /* Line1,
   Line2 */

DML Commands

1. INSERT

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

Note: Column names are optional.

Example

INSERT INTO EMPLOYEE VALUES (0001, 'Ava', 'Sales');

2. SELECT

SELECT column1, column2, ...
FROM table_name
[where condition];

Example

SELECT * FROM EMPLOYEE where dept ='sales';

3. UPDATE

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

Example

UPDATE EMPLOYEE SET dept = 'Sales' WHERE empId='0001';

4. DELETE

DELETE FROM table_name where condition;

Example

DELETE from EMPLOYEE where empId='0001';

Indexes

1. CREATE INDEX

  CREATE INDEX index_name on table_name(column_name);

To Create Unique index:

  CREATE UNIQUE INDEX index_name on table_name(column_name);

2. DROP INDEX

DROP INDEX index_name ON table_name;

Views

1. Create a View

Creating a View:
CREATE VIEW View_name AS 
Query;

2. How to call view

SELECT * FROM View_name;

3. Altering a View

ALTER View View_name AS 
Query;

4. Deleting a View

DROP VIEW View_name;

Triggers

1. Create a Trigger

CREATE TRIGGER trigger_name trigger_time trigger_event
    ON tbl_name FOR EACH ROW [trigger_order] trigger_body
/* where
trigger_time: { BEFORE | AFTER }
trigger_event: { INSERT | UPDATE | DELETE }
trigger_order: { FOLLOWS | PRECEDES } */

2. Drop a Trigger

DROP TRIGGER [IF EXISTS] trigger_name;

Stored Procedures

1. Create a Stored Procedure

CREATE PROCEDURE sp_name(p1 datatype)
BEGIN
/*Stored procedure code*/
END;

2. How to call Stored procedure

CALL sp_name;

3. How to delete stored procedure

DROP PROCEDURE sp_name;

Joins

1. INNER JOIN

SELECT * FROM TABLE1 INNER JOIN TABLE2 where condition;

2. LEFT JOIN

SELECT * FROM TABLE1 LEFT JOIN TABLE2 ON condition;

3. RIGHT JOIN

SELECT * FROM TABLE1 RIGHT JOIN TABLE2 ON condition;

4. CROSS JOIN

SELECT select_list from TABLE1 CROSS JOIN TABLE2;