added joins and updated readme

Author: AnuragAnalog

README.md

@@ -137,6 +137,16 @@ delete from employee where employee_id = 2;
 delete from employee;
 ```
 
+#### Enabling foreign key checks
+```sql
+set foreign_key_checks = 1;
+```
+
+#### Disabling foreign key checks
+```sql
+set foreign_key_checks = 0;
+```
+
 ## Data Query Language (DQL)
 
 #### Display Table
@@ -179,4 +189,27 @@ delete from personal_info where age < 40;
 #### Droping a view
 ```sql
 drop view personal_info;
+```
+
+## Joins
+#### Inner join
+```sql
+select e.fname, p.pname from employees as e inner join project as p on e.eid = p.eid;
+```
+
+#### Full outer join
+```sql
+select e.fname, p.pname from employees as e left outer join project as p on e.eid = p.eid
+union
+select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid;
+```
+
+#### Left outer join
+```sql
+select e.fname, p.pname from employees as e left outer join project as p on e.eid = p.eid;
+```
+
+#### Right outer join
+```sql
+select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid;
 ```

joins.sql

@@ -0,0 +1,58 @@
+
+-- creating basic stuff to work on them
+create database cheatsheet;
+use cheatsheet;
+
+create table employees
+(
+    eid int primary key,
+    fname varchar(20),
+    lname varchar(20),
+    salary real,
+    joindate date,
+    dept varchar(10),
+    gender char
+);
+
+create table project
+(
+    pid int primary key,
+    eid int,
+    pname varchar(20)
+);
+
+alter table project add foreign key(eid) references employees(eid);
+
+set foreign_key_checks = 0;
+
+insert into employees values (1, "Vikas", "Ahlawat", 600000, "2013-02-15", "IT", "M");
+insert into employees values (2, "nikita", "Jain", 530000, "2014-01-09", "HR", "F");
+insert into employees values (3, "Ashish", "Kumar", 1000000, "2014-01-09", "IT", "M");
+insert into employees values (4, "Nikhil", "Sharma", 480000, "2014-01-09", "HR", "M");
+insert into employees values (5, "anish", "kadian", 500000, "2014-01-09", "Payroll", "M");
+
+insert into project values (1, 1, "Task Track");
+insert into project values (2, 1, "CLP");
+insert into project values (3, 1, "Survey Management");
+insert into project values (4, 2, "HR Management");
+insert into project values (5, 3, "Task Track");
+insert into project values (6, 3, "GRS");
+insert into project values (7, 3, "DDS");
+insert into project values (8, 4, "HR Management");
+insert into project values (9, 6, "GL Management");
+
+set foreign_key_checks = 1;
+
+-- inner join
+select e.fname, p.pname from employees as e inner join project as p on e.eid = p.eid;
+
+-- outer join
+select e.fname, p.pname from employees as e left outer join project as p on e.eid = p.eid
+union
+select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid;
+
+-- left outer join
+select e.fname, p.pname from employees as e left outer join project as p on e.eid = p.eid;
+
+-- right outer join
+select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid;