SQL query is used to fetch data from the database. In some of the scenario you may need some perquisite data to call subsequent SQL query to fetch data from a table so instead of writing two seperate query we can write SQL query within the query.Therefore subQuery is a way to combine or join them in single query. Subqurey can have two types −Correlated subquery - In correlated subquery, inner query is dependent on the outer query. Outer query needs to be executed before inner queryNon-Correlated subquery - In non-correlated query inner query does not dependent on the outer query. ... Read More

In Hierarchical data model, relationship between table and data is defined in parent child structure. In this structure data are arranged in the form of a tree structure. This model supports one-to-one and one-to-many relationships.On the other hand, network model arrange data in graph structure. In this model each parents can have multiple children and children can also have multiple parents. This model supports many to many relationships also.Sr. No.KeyHierarchical Data ModelNetwork Data Model1Basic Relationship between records is of the parent child typeRelationship between records is expressed in the form of pointers or links.2        Data Inconsistency It can have data ... Read More

Union is a set operator that can be used to combine the result set of two different SELECT statement. In the union number of columns and data type should be the same. It has two types −UnionUnion All On the other hand ,In a Relational database, tables are associated with each other and we used foreign key to maintain relationships between tables. We used join clause to retrieve data from associated tables. The join condition indicates how column in each table are matched against each other. There are two types of joins clause in SQL Inner join Outer join Sr. No.KeyJoinUNION1Basic It can be used to ... Read More

In Relational database tables are associated with each other and we used foreign key to maintain relationships between tables. We used join clause to retrieve data from associated tables. The join condition indicates how column in each table are matched against each other. There are two types of joins clause in SQL Inner join Outer joinOuter join is again divided into parts −LEFT OUTER JOIN - It will return all data of the left table and matched  records in both table RIGHT OUTER JOIN - it will return all the data of the right table and matched records in both tableSr. No.KeyInner joinOuter join1Basic It ... Read More

In the relationaltonal database key is the most important element to maintain the relationship between two tables or to uniquely identify data from the table. Primary key is used to identify data uniquely therefore two rows can’t have the same primary key. It can’t be null.On the other hand, foreign key is used to maintain relationship between two tables. Primary of a table act as forgein key in the other table. Foreign key in a table enforce Referential Integrity constraint. It can be more than one in the table.Sr. No.KeyPrimary KeyForeign Key1Basic It is used to uniquely identify data in the ... Read More

Both the TRUNCATE statement and the DELETE statement are included in the category of SQL queries for deleting the data stored in a table. They carry out deletion operations on records or rows of a table that are no longer needed. A condition is applied before each entry in the table that is being deleted when using the DELETE command. To put it another way, it is possible to delete one or more rows all at once. However, with the TRUNCATE command, each row is removed from the table simultaneously. When we delete something using the DELETE query, a log ... Read More

What is NoSQL?As per the official Wiki definition: “A NoSQL (originally referring to “non SQL” or “non relational”) database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relation databases (RDBMS). It encompasses a wide variety of different database technologies that were developed in response to a rise in the volume of data stored about users, objects and products, the frequency in which this data is accessed, and performance and processing needs. Generally, NoSQL databases are structured in a key-value pair, graph database, document-oriented or column-oriented structure.Over decades ... Read More

SQL (Structured Query Language) is a computer language which is used to interact with an RDBMS (Relational Database Management System). It is basically a method of managing, organizing, and retrieving data from a relation database. In SQL, two important concepts are used namely, function and procedure. A function calculates the results of a program based on the inputs provided, whereas a procedure is used to perform some tasks in a specific order. There are many other differences between functions and procedures, which we will discuss in this article. What is Function? A function, in the context of computer programming languages, ... Read More

Both Primary key and Unique key both are used to identify records uniquely in a table. These keys are also used to create relationship between tables. A table can have only one primary key whereas there can be multiple unique keys in a single table or relation. Read this tutorial to learn more about primary keys and unique keys and how they are different from each other. What is Primary Key? A primary key is a column or set of columns that uniquely identifies each row in a table. It must be unique across all rows in the table. A ... Read More

PL/SQL stands for “Procedural Language extension to SQL” . It is the mixture of SQL and Procedural features provided by programming language. It was developed by Oracle Corporation in the late 1980s as procedural extension language for SQL and the Oracle relational database.PL/SQL programs consists of blocks that can be nested and a block structure look likes this −DECLARE    -- it contains declaration statements BEGIN    -- It contains executable statements EXCEPTIONS    -- It contains exception handling statements END;ExampleIn PL/SQL single-line comments begin with double hyphen(--) and Multi-line comments begin with a slash-asterisk ( /* ) and end ... Read More