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MySQL Database Terminology

One of the freely available, reliable and popular databases is MySQL and we will be studying more about same in this series.

Before we proceed to explain the MySQL database system, let us have a look at few definitions related to the database which are in general applicable to any other relational databases as well.

  1. Database - A database is a collection of tables, with related data.

  2. Table - A table is a matrix with data. A table in a database looks like a simple spreadsheet.

  3. Column - One column (data element) contains data of one and the same kind, for example, the column postcode.

  4. Row - A row (= tuple, entry or record) is a group of related data, for example, the data of one subscription.

  5. Redundancy - Storing data twice in more than one tables, redundantly to make the system faster.

  6. Primary Key - A primary key is unique. A key value can not occur twice in one table. With a key, you can only find one row. A table will have only one Primary Key

  7. Unique Key - A unique key is a combination of one or more columns which can uniquely identify a row in the table. That combination cannot occur more than once in one table excluding rows having NULL values in key columns. A table can have more than one unique key.

  8. Compound Key - A compound key (composite key) is a key that consists of multiple columns because one column is not sufficiently unique. Another term for the unique key which has more than one column.

  9. Foreign Key - A foreign key is a linking pin between two tables.

  10. Index - An index in a database resembles an index at the back of a book.

  11. Referential Integrity - Referential Integrity makes sure that a foreign key value always points to an existing row.


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