MySQL databases are relational.
A relational database stores data in separate tables rather than putting all the data in one big
storeroom. The database structures are organized into physical files optimized for speed. The
logical model, with objects such as databases, tables, views, rows, and columns, offers a flexible
programming environment. You set up rules governing the relationships between different data
fields, such as one-to-one, one-to-many, unique, required or optional, and “pointers” between
different tables. The database enforces these rules, so that with a well-designed database, your
application never sees inconsistent, duplicate, orphan, out-of-date, or missing data.
The SQL part of “MySQL” stands for “Structured Query Language”. SQL is the most common
standardized language used to access databases. Depending on your programming environment,
you might enter SQL directly (for example, to generate reports), embed SQL statements into code
written in another language, or use a language-specific API that hides the SQL syntax.
SQL is defined by the ANSI/ISO SQL Standard. The SQL standard has been evolving since 1986
and several versions exist. In this manual, “SQL-92” refers to the standard released in 1992,
“SQL:1999” refers to the standard released in 1999, and “SQL:2003” refers to the current version
of the standard. We use the phrase “the SQL standard” to mean the current version of the SQL
Standard at any time.
... zobacz całą notatkę