SSC CGL Exam > SSC CGL Videos > SSC CGL Tier 2 - Study Material, Online Tests, Previous Year > Constraints and Database Schemas
Constraints and Database Schemas Video Lecture | SSC CGL Tier 2 - Study Material, Online Tests, Previous Year
FAQs on Constraints and Database Schemas Video Lecture - SSC CGL Tier 2 - Study Material, Online Tests, Previous Year
| 1. What are constraints in a database schema? |  |
Ans. Constraints in a database schema are rules or conditions that are imposed on the data stored in a database. They ensure that the data follows certain criteria or relationships, maintaining the integrity and consistency of the database. Constraints can include rules such as unique values, primary key constraints, foreign key constraints, and check constraints.
| 2. How do constraints help in maintaining data integrity? | |
Ans. Constraints play a crucial role in maintaining data integrity in a database. They enforce rules and conditions on the data, preventing it from being inserted, updated, or deleted in a way that violates the defined criteria. Constraints such as unique constraints ensure that each value in a column is unique, while foreign key constraints maintain referential integrity by enforcing relationships between tables.
| 3. What is the difference between primary key and foreign key constraints? | |
Ans. A primary key constraint is used to uniquely identify each record in a table. It ensures that the values in the specified column(s) are unique and cannot be null. On the other hand, a foreign key constraint establishes a relationship between two tables. It enforces referential integrity by ensuring that the values in a column of one table match the values in another table's primary key column.
| 4. How do check constraints work in a database schema? | |
Ans. Check constraints allow the definition of conditions that the data must meet before being inserted or updated in a table. These conditions can be based on logical expressions, comparisons, or patterns. Check constraints are used to restrict the values that can be stored in a column, ensuring that they meet specific criteria.
| 5. Can constraints be modified or dropped after they are created? | |
Ans. Yes, constraints can be modified or dropped after they are created. In most database management systems, there are commands or statements available to alter or drop constraints. However, it is important to consider the impact of modifying or dropping constraints on the data integrity and consistency of the database. It is recommended to carefully evaluate and plan any changes to constraints before implementing them.
Text Transcript from Video
hello friends welcome back in this
tutorial we will study about constraints
on databases there are many restrictions
or constraints on the actual values in a
database state constraints on databases
can be divided into three categories
first is inherent model based
constraints or implicit constraints
these are the constraints that are
inherent in the data model for example
the constraint that a relation cannot
have duplicate tuples is an inherent
constraint of the relational model
second is a schema based constraints or
explicit constraints a schema based
constraints are explicit constraints are
constraints that can be directly
expressed in the schema of the data
model by specifying them in the DDL for
example key constraints domain
constraints and entity integrity
constraints are constraints that can be
expressed in a schema of the relational
model domain constraints are schema
based constraints of the relational
model domain constraints specify that
within each tuple the value of each
attribute a must be an atomic value from
the domain of attribute P
third is application-based
our semantic constraints these are the
constraints that cannot be directly
expressed in the schema of the data
model so they must be expressed and
enforced by the application programs
thank you very much
tutorial we will study about constraints
on databases there are many restrictions
or constraints on the actual values in a
database state constraints on databases
can be divided into three categories
first is inherent model based
constraints or implicit constraints
these are the constraints that are
inherent in the data model for example
the constraint that a relation cannot
have duplicate tuples is an inherent
constraint of the relational model
second is a schema based constraints or
explicit constraints a schema based
constraints are explicit constraints are
constraints that can be directly
expressed in the schema of the data
model by specifying them in the DDL for
example key constraints domain
constraints and entity integrity
constraints are constraints that can be
expressed in a schema of the relational
model domain constraints are schema
based constraints of the relational
model domain constraints specify that
within each tuple the value of each
attribute a must be an atomic value from
the domain of attribute P
third is application-based
our semantic constraints these are the
constraints that cannot be directly
expressed in the schema of the data
model so they must be expressed and
enforced by the application programs
thank you very much
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