You probably already know that a primary key is used to uniquely identify a row of data in a table. In some cases, one column in the table can server as a primary key. In other cases, it takes multiple columns to serve as a primary key. Any primary key based on two or more columns is called a composite primary key.
The columns in a table are often called fields or attributes of the entity the table represents. Each row in that table is called a record or tuple. The word "tuple" is most commonly used in relational data theory. Most practitioners use "record" or "row" instead of "tuple."
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