User-Defined Integrity − Enforces some specific business rules that do not fall into entity, domain or referential integrity.ĭatabase normalization is the process of efficiently organizing data in a database. Referential integrity − Rows cannot be deleted, which are used by other records. The following categories of data integrity exist with each RDBMS −Įntity Integrity − 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. INDEX − Used to create and retrieve data from the database very quickly. PRIMARY Key − Uniquely identifies each row/record in a database table.įOREIGN Key − Uniquely identifies a row/record in any another database table.ĬHECK Constraint − The CHECK constraint ensures that all values in a column satisfy certain conditions. UNIQUE Constraint − Ensures that all the values in a column are different. NOT NULL Constraint − Ensures that a column cannot have a NULL value.ĭEFAULT Constraint − Provides a default value for a column when none is specified. 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 − 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. SQL ConstraintsĬonstraints are the rules enforced on data columns on a table. 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 column?Ī column is a vertical entity in a table that contains all information associated with a specific field in a table.įor example, a column in the CUSTOMERS table is ADDRESS, which represents location description and would be as shown below −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. Following is a single row of data or record in the CUSTOMERS table −Ī 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. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.Ī field is a column in a table that is designed to maintain specific information about every record in the table.
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |Įvery table is broken up into smaller entities called fields. The following program is an example of a CUSTOMERS table − 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 which are called 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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