The difference between Having and Where clause is one of the most commonly asked database interview questions. The most answer by many aspiring developers is Where clause is used to select any queries while Having clause is used in queries containing aggregate function. Both definitions are correct but when they are asked to explain the […]
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Difference Between Inner and Outer Join
Joins in SQL table are used to combine the data present in two different tables and display the result in a single table. The table which displays the result of join is temporary; the resultant table will be based on the comparison of columns between the tables. The effectiveness of joins are based on the […]
Difference Between Subquery and Derived Tables
What is Subquery? Subqueries are defined as the queries which are used inside a query. Subqueries are commonly used along with WHERE clause to filter the rows returned from the outer query. Subqueries are classified as a SELECT statement which can be nested with other statements. Read: What is meant by inner join and outer? […]
Types of Indexes in SQL
Indexes in database are used to accelerate the data retrieval process. Queries like SELECT and WHERE clauses can be accelerated using indexes but they ultimately slow down UPDATE and INSERT statements. Index creation has no effect on the data present in a table. The CREATE INDEX statement is used create an index; CREATE INDEX statement […]
What is Bitmap Index?
Bitmap index in a Oracle database is special type of database index which is used to reduce cardinality of columns. The columns with lower cardinality value will result in result in relatively unique values. Consider that there is a column called binary digits; this column will have only two values namely 0 and 1. The […]
What is Superkey?
Super key in database can be defined as the combination of fields which can be used to uniquely identify a row present in a table. A unique super key is used for each and every row present in a RDBMS table. At least one field in a superkey must have value while the rest can […]
What is SQL Server Transaction?
Transactions in SQL server is a process of grouping a tasks inside a single execution unit. Every SQL transaction starts with a specific task. Transactions are declared as over when the tasks are grouped successfully. The result of transactions is always binary and incomplete statements will result in transaction failure. The statements given below are […]
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