HSQLDB supports various types of constraints to enforce data integrity rules on database tables. Here are the different types of constraints supported by
HSQLDB :
Primary Key Constraint :
* A primary key constraint ensures that each row in a table has a unique identifier.
* It uniquely identifies each row and prevents duplicate values in the specified column or columns.
* You can define a primary key constraint using the PRIMARY KEY keyword when creating a table or by altering an existing table.
Foreign Key Constraint :
* A foreign key constraint establishes a relationship between two tables by enforcing referential integrity.
* It ensures that values in a column (or columns) in one table match values in a corresponding column (or columns) in another table.
* You can define a foreign key constraint using the FOREIGN KEY keyword when creating a table or by altering an existing table.
Unique Constraint :
* A unique constraint ensures that values in a column (or columns) are unique across all rows in a table.
* It prevents duplicate values in the specified column or columns but allows null values.
* You can define a unique constraint using the UNIQUE keyword when creating a table or by altering an existing table.
Check Constraint :
* A check constraint enforces a condition on the values in one or more columns in a table.
* It allows you to specify a Boolean expression that must evaluate to true for all rows in the table.
* You can define a check constraint using the CHECK keyword when creating a table or by altering an existing table.
Not Null Constraint :
* A not null constraint ensures that a column does not contain null values.
* It requires that all values in the specified column are non-null.
* You can define a not null constraint using the NOT NULL keyword when creating a table or by altering an existing table.
