![]() Referential integrity − Rows cannot be deleted, which are used by other records. The following categories of data integrity exist with each RDBMS −Įntity Integrity − This ensures that there are no duplicate rows in a table.ĭomain Integrity − Enforces valid entries for a given column by restricting the type, the format, or the range of values. Used to create and retrieve data from the database very quickly. Uniquely identifies a row/record in any another database table.Įnsures that all values in a column satisfy certain conditions. Uniquely identifies each row/record in a database table. Provides a default value for a column when none is specified.Įnsures that all the values in a column are different. ![]() Column level constraints are applied only to one column whereas, table level constraints are applied to the entire table.įollowing are some of the most commonly used constraints available in SQL − S.No.Įnsures that a column cannot have a NULL value. This ensures the accuracy and reliability of the data in the database.Ĭonstraints can either be column level or table level. These are used to limit the type of data that can go into a table. IDĬonstraints are the rules enforced on data columns on a table. Following table has three records where first record has NULL value for the salary and second record has a zero value for the salary. A field with a NULL value is the one that has been left blank during a record creation. It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. What is a NULL value?Ī NULL value in a table is a value in a field that appears to be blank, which means a field with a NULL value is a field with no value. What is a column?Ī column is a vertical entity in a table that contains all information associated with a specific field in a table.įor example, our CUSTOMERS table have different columns to represent ID, Name, Age, Salary, City and Country. Following is a single row of data or record in the CUSTOMERS table − IDĪ record is a horizontal entity in a table. For example, there are 7 records in the above CUSTOMERS table. What is a Record or a Row?Ī record is also called as a row of data is each individual entry that exists in a table. A field is a column in a table that is designed to maintain specific information about every record in the table.įor example, our CUSTOMERS table consists of different fields like ID, Name, Age, Salary, City and Country. Following is an example of a CUSTOMERS table which stores customer's ID, Name, Age, Salary, City and Country − IDĮvery table is broken up into smaller entities called fields. Remember, a table is the most common and simplest form of data storage in a relational database. ![]() This table is basically a collection of related data entries and it consists of numerous columns and rows. The data in an RDBMS is stored in database objects known as tables. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.Ī Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. RDBMS stands for Relational Database Management System.
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