PHP connection to MySQL database Basics

BoolDefine(String name, mixed value [, bool case_insensitive])
The define function defines constants.

define('DB_HOST', 'localhost');define('DB_USER', 'root');define('DB_PWD', '123456');define('DB_NAME', 'mtest');

ResourceMysql_connect([String server [, string username [, string password [, bool new_link [, int client_flags])
The mysql_connect function is used to open or reuse a connection to the MySQL server.

$conn = mysql_connect('DB_HOST', 'DB_USER', 'DB_PWD');

ResourceMysql_query(String Query [, resource link_identifier])
The mysql_query function sends a query to the active database on the server associated with the specified connection identifier.
Mysql_query () Only returns a resource identifier for select, show, explain or describe statements. If the query execution is incorrect, false is returned. For other types of SQL statements, if mysql_query () is executed successfully, true is returned. If an error occurs, false is returned. If the return value is not false, the query is legal and can be executed by the server. This does not indicate any affected or returned number of rows. It is very likely that a query is successfully executed but does not affect or no rows are returned.

 $query = 'select * from message'; $result = mysql_query($query);

 

ArrayMysql_fetch_array(Resource result [, int result_type])
The mysql_fetch_array function is used to obtain a row from the result set as an associated array, or a number array, or both. If there are no more rows, returnFalse.
Mysql_fetch_array ($ result, mysql_num) ====== mysql_fetch_array ($ result)
Mysql_fetch_array ($ result, mysql_assoc) ======= mysql_fetch_assoc ($ result)

mysql_fetch_array($result, MYSQL_ASSOC)

BoolMysql_free_result(Resource result)
The mysql_free_result function is used to call mysql_free_result () only when considering how much memory will be occupied when a large result set is returned. After the script is completed, all associated memory will be automatically released. If the call succeeds, true is returned. If the call fails, false is returned.

mysql_free_result($result);

BoolMysql_close([Resource link_identifier])
The mysql_close function is used to close the non-persistent connection associated with the specified connection ID to the MySQL server. If link_identifier is not specified, the last opened connection is closed. Generally, mysql_close () is not required, because the opened non-persistent connection is automatically closed after the script is executed.

mysql_close($conn);

Example:

define('DB_HOST', 'localhost');define('DB_USER', 'root');define('DB_PWD', '123456');define('DB_NAME', 'mtest');$conn = mysql_connect('DB_HOST', 'DB_USER', 'DB_PWD');mysql_select_db(DB_NAME, $conn);mysql_query('SET NAMES UTF8');$query = 'select * from message';$result = mysql_query($query);mysql_fetch_array($result, MYSQL_ASSOC);mysql_free_result($result);mysql_close($conn);