Constraints
NOT NULL CONSTRAINT - Ensures that a column cannot have a null value. DEFAULT CONSTRAINT - Provides a default value for a column when none is specified UNIQUE CONSTRAINT - Ensures that all values in columns are different CHECK CONSTRAINT - Makes sure that all values in a column satisfy certain criteria PRIMARY KEY CONSTRAINT - Used to uniquely identify a row in the table FOREIGN KEY CONSTRAINT - Used to ensure referential integrity of the data Primary Key - is used uniquely to identify each row in a table . It can consist of one or more columns on a table . When Multiple columns are used on a table it is called composite key. Foreign Key - Foreign key is a column or columns that references a column most often primary key of another table . The purpose of foreign key is to maintain referential integrity of the data. Pg admin Data base - training - right click on training - query click Always add semi colen to run the query Int - integer varchar - variable charact