added some more joins

Author: AnuragAnalog

README.md

@@ -195,6 +195,10 @@ drop view personal_info;
 #### Inner join
 ```sql
 select e.fname, p.pname from employees as e inner join project as p on e.eid = p.eid;
+
+-- or
+
+select e.fname, p.pname from employees as e join project as p on e.eid = p.eid;
 ```
 
 #### Full outer join
@@ -214,6 +218,16 @@ select e.fname, p.pname from employees as e left outer join project as p on e.ei
 select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid;
 ```
 
+#### Left outer join - inner join
+```sql
+select e.fname, p.pname from employees as e left outer join project as p on e.eid = p.eid where p.pname is null;
+```
+
+#### Right outer join - inner join
+```sql
+select e.fname, p.pname from employees as e right outer join project as p on e.eid = p.eid where e.fname is null;
+```
+
 ## Aggregation
 
 #### Sum function
@@ -353,6 +367,11 @@ select rand();
 select cast(23.01245 as signed);
 ```
 
+#### Concatenation
+```sql
+select concat("Mahesh", " ", "Chandra", " ", "Duddu", "!");
+```
+
 #### Extract Month
 ```sql
 select month("1998-12-30");