JOIN's is used to query data from two or more than two table based on relationship between certain columns in these tables. Tables in Database are related to each other with some constraints like (Primary Key & Foreign Key) Primary Key :- Column with unique value for each row that is not value matching to each other in the column. Foreign Key :- Two tables are mapped through concept of primary and foreign key, that means primary key of one table is used in other table as foreign key. fig : Primary Key and Foreign Key Example Query to create the above two tables. CREATE TABLE `project_mst` ( `PK_PROJECT_ID` varchar(10) NOT NULL, `PROJECT_NAME` varchar(100) default NULL, `PROJECT_DURATION` varchar(50) default NULL, `FK_MANAGER_ID` varchar(10) default NULL, PRIMARY KEY (`PK_PROJECT_ID`) ) CREATE TABLE `manager_mst` ( `PK_MANAGER_ID` varchar(10) NOT NULL, `MANAGER_...