What are the SQL constraints and types.

Question

Accepted Answer

SQL constraints are rules that are applied to columns in a table to ensure data integrity and consistency.

SQL constraints are used to enforce rules on the data stored in tables.
They can be applied to individual columns or the entire table.
Common types of SQL constraints include primary key, foreign key, unique, not null, and check constraints.
Primary key constraints ensure that each row in a table is uniquely identified.
Foreign key constraints establish relationships between tables.
Unique constraints ensure that values in a column are unique.
Not null constraints enforce that a column cannot have null values.
Check constraints define conditions that must be met for data to be valid.
Constraints can be added during table creation or altered later using SQL statements.

Accepted Answer

Primary key,foriegn key,default.

Accepted Answer

Constraints can be specified when the table is created with the CREATE TABLE statement, or after the table is created with the ALTER TABLE statement.

The following constraints are commonly used in SQL:

NOT NULL - Ensures that a column cannot have a NULL val

UNIQUE - Ensures that all values in a column are differen

PRIMARY KEY - A combination of a NOT NULL and UNIQUE. Uniquely identifies each row in a tabl

FOREIGN KEY - Prevents actions that would destroy links between table

CHECK - Ensures that the values in a column satisfies a specific conditio

DEFAULT - Sets a default value for a column if no value is specifie

CREATE INDEX - Used to create and retrieve data from the database very quickly.

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