Mysql数据库
A database is a separate application that stores a collection of data. Each database has one or more distinct APIs for creating, accessing, managing, searching and replicating the data it holds.
Other kinds of data stores can be used, such as the file system or large hash tables in memory but data fetching and writing would not be so fast and easy with those types of systems.
RDBMS: relational database management systems. This is called relational database because all the data is stored into different tables and **relations are established using primary keys **or other keys known as foreign keys.
RDBMS: Enables you to implement a database with tables, columns and indexes. Guarantees the Referential Integrity between rows of various tables. Updates the indexed automatically. Interprets an SQL query and combines information from various tables.
Revise few definitions:
Database: A collection of tables, with related data. Table: a matrix with data. Column: One column contains data of one and the same kind. Row: a row is a group of related data. Redundancy: Storing data twice, redundantly to make the system faster. Primary Key: A primary key is unique. A key value can not occur twice in one table. With a key, you can find at most one row. Foreign Key: A foreign key is the linking pin between two tables. Compound Key: A compound key is a key that consists of multiple columns, because one column is not sufficiently unique.
Index: An index in a database resembles an index at the back of a book.
Referential Integrity: Referential Integrity makes sure that a foreign key value always points to an existing row.
MySQL supports large databases, up to 50 million rows or more in a table. The default file size limit for a table is 4GB, but you can increase this (if your operating system can handle it) to a theoretical limit of 8 million terabytes (TB).
