 

create table tblEmployee
(
emp_id int primary key,
emp_name varchar(30) not null,
dept_id int not null,
manager_id int not null,
salary int not null);

create table Dept
(
dept_id int primary key,
dept_name varchar(30) not null);

insert into tblEmployee values
(1, 'Sumit', 1, 3, 2999),
(2, 'Reshma', 1, 3, 3999),
(3, 'Farhana', 2, 5, 1000),
(4, 'Robin', 1, 5, 2000),
(5, 'Robin', 2, 0, 3000),
(6, 'Robin', 1, 2, 2000);

insert into Dept values
(1, 'IT'),
(2, 'Admin');


-- get All the duplicate records
--    select 
      -- emp_name, salary, count(*) 
      -- from tblEmployee 
      -- group by emp_name, salary 
      -- having count(*)>1;

-- get The list of employees managers
-- select
--     e.emp_id, e.emp_name, m.emp_name as manager_name
--     from tblEmployee e
--     LEFT JOIN tblEmployee m
--     on e.manager_id = m.emp_id;    

-- get nth highest Salary
-- select emp_id, emp_name, salary 
--       from tblEmployee 
--       order by salary desc limit 1,1;

-- rank By salary alternative using window function
-- with ranking as(
-- select
--       emp_id, emp_name, salary,
--       DENSE_RANK() 
--       OVER(ORDER BY salary desc) rank_by_salary
--       from tblEmployee
-- )
-- select emp_id, emp_name, salary 
--       from ranking 
--       where rank_by_salary=4 LIMIT 1;

-- get nth Highest Salary separated by departments using DENSE_RANK() window function
-- with deptSep as(
--   select emp_id, emp_name, salary, dept_id,
--       DENSE_RANK() OVER (PARTITION BY dept_id 
--       ORDER BY salary desc) dept_separated_rank
--       from tblEmployee
-- )
-- select emp_id, emp_name, salary, dept_id 
--       from deptSep
--       where dept_separated_rank=2;


-- UNION ALL will show both the records and will not exclude the common records as the regular UNION
-- select dept_name 
--       from Dept d
--       where d.dept_name="IT"
--       union all
-- select dept_name 
--       from Dept d
--       where d.dept_name="IT";

-- get The department who have less than 3 Employees
-- select e.dept_id, d.dept_name
--       from tblEmployee e
--       join Dept d 
--       on e.dept_id = d.dept_id
--       GROUP BY e.dept_id, d.dept_name 
--       HAVING COUNT(e.emp_id) < 3;

created 3 years ago

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;