Category: DBMS

This is how we can find the nth highest salary in SQL SERVER using TOP keyword: SELECT TOP 1 salary FROM ( SELECT DISTINCT TOP N salary FROM Employee ORDER BY salary DESC ) AS temp ORDER BY salary This is how we can find the nth highest salary in MYSQL using LIMIT keyword: SELECT salary FROM Employee ORDER BY salary DESC LIMIT N-1, 1 ... Read Mores

To insert multiple rows in SQL we can follow the below syntax: INSERT INTO table_name (column1, column2,column3...) VALUES (value1, value2, value3…..), (value1, value2, value3….), ... (value1, value2, value3); We start off by giving the keywords INSERT INTO then we give the name of the table into which we would want to insert the values. We will follow it up with the list of the columns, for which we would have to add the values. Then we will give in the VALUES key... Read Mores

A trigger is a stored program in a database which automatically gives responses to an event of DML operations done by insert, update, or delete. In other words, is nothing but an auditor of events happening across all database tables. Let’s look at an example of a trigger : CREATE TRIGGER bank_trans_hv_alert BEFORE UPDATE ON bank_account_transaction FOR EACH ROW begin if( abs(:new.transaction_amount)>999999)THEN RAISE_APPLICATION_ERROR(-20000, 'Account transaction exceedi... Read Mores

Unique Key is a constraint in SQL. So, before understanding what exactly is a primary key, let’s understand what exactly is a constraint in SQL. Constraints are the rules enforced on data columns on a table. These are used to limit the type of data that can go into a table. Constraints can either be column level or table level. Unique Key:  Whenever we give the constraint of unique key to a column, this would mean that the column cannot have any duplicate values present in it. In other ... Read Mores

To delete a column in SQL we will be using DROP COLUMN method: ALTER TABLE employees DROP COLUMN age; We will start off by giving the keywords ALTER TABLE, then we will give the name of the table, following which we will give the keywords DROP COLUMN and finally give the name of the column which we would want to remove.... Read Mores

Our database comprises of a lot of different entities such as tables, stored procedures, functions, database owners and so on. To make sense of how all these different entities interact, we would need the help of schema. So, you can consider schema to be the logical relationship between all the different entities which are present in the database. Once we have a clear understanding of the schema, this helps in a lot of ways: We can decide which user has access to which tables in the data... Read Mores

OLAP stands for Online Analytical Processing. And a class of software programs which are characterized by relatively low frequency of online transactions. Queries are often too complex and involve a bunch of aggregations.... Read Mores

Data Integrity is the assurance of accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes, or retrieves data. It also defines integrity constraints to enforce business rules on the data when it is entered into an application or a database.... Read Mores

OLTP stands for Online Transaction Processing. And is a class of software applications capable of supporting transaction-oriented programs. An essential attribute of an OLTP system is its ability to maintain concurrency... Read Mores

Triggers may implement DML by using INSERT, UPDATE, and DELETE statements. These triggers that contain DML and find other triggers for data modification are called Nested Triggers.... Read Mores