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key It is used to uniquely identify any record or row of data from the table. It is also used to establish and identify relationships between tables. In the PERSON table, passport_number, license_number, SSN are keys since they are unique for each person. Primary key - It is the first key used to identify one and only one instance of an entity uniquely. An entity can contain multiple keys, as we..

The primary key is the criteria of the table. In other words, criteria table key is primary key. - Example1 : When join parent table with child table 1, primary key of parent table is a criteria key. Parent Table Primary Key Foreign Key Join : Primary KeyForeign Key Child Table 1 Primary Key Foreign Key - Example2 : When join child table 1 with child table 2, primary key of child table1 is a cri..