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Hello Guys, you might have heard about how useful the EXISTS clause is helpful in writing sophisticated queries. Still, at the same time, I have also seen that many programmers struggle to understand and use EXISTS and NOT EXISTS clause while writing SQL queries.  If you are one of them, then you have come to the right place. Today you will learn how to use the EXISTS clause in SQL by picking up a real-world example and an excellent SQL exercise from the LeetCode. Suppose that a website contains two tables, the Customers table, and the Orders table. Can you write an SQL query to find all customers who have never ordered anything ? To solve this problem, you need to first think about data. For example, if a customer has never ordered anything means there won't be any record for him on the Orders table. Good job, half of the task is done. Now the second half is how do you check if there is a record or not for a particular customer?  That's where EXISTS and NOT EXISTS clause will...

Truncate and delete in SQL are two commands which are used to remove or delete data from a table. Though quite basic in nature both SQL commands can create a lot of trouble until you are familiar with details before using it. The difference between Truncate and delete are not just important to understand perspective but also a very popular SQL interview topic which in my opinion a definite worthy topic. What makes them tricky is the amount of data. Since most Electronic trading system stores, large amounts of transactional data, and some even maintain historical data, a good understanding of delete and the truncate command is required to effectively work in that environment. I have still seen people firing delete commands just to empty a table with millions of records which eventually lock the whole table for doing anything and take ages to complete or Simply blew log segment or hang the machine. Most of the enterprise stock trading system maintains two kinds of database one transa...