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  SQL SUBQUERY AND CO-RELATED SUBQUERY IN ORACLE. Hello Everyone, Today I will give you the overview of Sub query and CO-RELATED Sub Query. Before starting this topic I suggest you to please go through my previous blogs related with SQL joins and types of Join, Classification of SQL and various commands in SQL. Before knowing SUBQUERY and CO-RELATED SUBQUERY first need to understand query. Query :   A query is basically used to request data or information from database tables or combination of tables to display the result .   In another word Data will be generated as a result used by SQL (Structure Query Language). In SQL statement we use select clause to fetch the data, from clause to pull data from the table and where clause to filter the result/output. For Example : If I need student_name from student table who lives in Delhi we need to query the data from student table.   To get the result we use the below query : Select student_name from student where location=’Delhi