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Internals and Portability

• Written in C and C++.

• Tested with a broad range of different compilers.

• Works on many different platforms. See https://www.mysql.com/support/supportedplatforms/

database.html. • For portability, configured using CMake. • Tested with Purify (a commercial memory leakage detector) as well as with Valgrind, a GPL tool

(http://developer.kde.org/~sewardj/).

• Uses multi-layered server design with independent modules.

• Designed to be fully multithreaded using kernel threads, to easily use multiple CPUs if they are

available.

• Provides transactional and nontransactional storage engines.

• Uses very fast B-tree disk tables (MyISAM) with index compression.

• Designed to make it relatively easy to add other storage engines. This is useful if you want to provide

an SQL interface for an in-house database.

• Uses a very fast thread-based memory allocation system.

• Executes very fast joins using an optimized nested-loop join.

• Implements in-memory hash tables, which are used as temporary tables.

• Implements SQL functions using a highly optimized class library that should be as fast as possible.

Usually there is no memory allocation at all after query initialization.

• Provides the server as a separate program for use in a client/server networked environment, and as

a library that can be embedded (linked) into standalone applications. Such applications can be used

in isolation or in environments where no network is available.

Data Types

• Many data types: signed/unsigned integers 1, 2, 3, 4, and 8 bytes long, FLOAT, DOUBLE, CHAR,

VARCHAR, BINARY, VARBINARY, TEXT, BLOB, DATE, TIME, DATETIME, TIMESTAMP, YEAR, SET,

ENUM, and OpenGIS spatial types. See Chapter 11, Data Types. • Fixed-length and variable-length string types.

Statements and Functions

• Full operator and function support in the SELECT list and WHERE clause of queries. For example:

mysql> SELECT CONCAT(first_name, ' ', last_name)

 -> FROM citizen

 -> WHERE income/dependents > 10000 AND age > 30;

• Full support for SQL GROUP BY and ORDER BY clauses. Support for group functions (COUNT(),

AVG(), STD(), SUM(), MAX(), MIN(), and GROUP_CONCAT()).

6

The Main Features of MySQL

• Support for LEFT OUTER JOIN and RIGHT OUTER JOIN with both standard SQL and ODBC

syntax.

• Support for aliases on tables and columns as required by standard SQL.

• Support for DELETE, INSERT, REPLACE, and UPDATE to return the number of rows that were

changed (affected), or to return the number of rows matched instead by setting a flag when

connecting to the server.

• Support for MySQL-specific SHOW statements that retrieve information about databases, storage

engines, tables, and indexes. Support for the INFORMATION_SCHEMA database, implemented

according to standard SQL.

• An EXPLAIN statement to show how the optimizer resolves a query.

• Independence of function names from table or column names. For example, ABS is a valid column

name. The only restriction is that for a function call, no spaces are permitted between the function

name and the “(” that follows it. See Section 9.3, “Keywords and Reserved Words”. • You can refer to tables from different databases in the same statement.

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