PHP4 and MySQL database operation function detailed explanation (ii)

<3> Select a database function (1):

mysql_select_db ()
Format: int mysql_select_db (string database name, int link_identifier);
Returns 1 false values if the specified database name is selected, succeeds, returns 1 Truth (True), and fails.

Example 1:
<?php
$select = mysql_select_db (' forum ', $connect);
if ($select)
{echo "Connect db forum successed!";}
Else
{echo "Connect db forum failed!";}
?>

Example 2:
<?php
$select = mysql_select_db ("forum", $connect) or Die ("Can not connect this db!");
?>

Note: This function is equivalent to the USE statement in MySQL: Use forum

<4>. SQL query Functions (2):

1, mysql_query ()
Format: int mysql_query (string sqlquery, int link_identifier);
Send a standard SQL statement request to the server. If it fails, a false value is returned.

Example:
<?php
$connect = mysql_connect ($hostname, $user, $pwd);
$select = mysql_select_db ($dbname, $connect);
$query = mysql_query ($sql, $connect);
if ($query) echo "Successed!";
else echo "Failed!";
?>
This function must be used in conjunction with the mysql_select_db () function, it is meaningless to use it alone!

2, Mysql_db_query ()
Format: int mysql_db_query (String database, string sqlquery, int link_identifier);

Database names and SQL statement sqlquery must be specified in this function, and False if failed.

Example:

<?php
$connect = mysql_connect ($hostname, $user, $pwd);
$query = Mysql_db_query ($dbname, $sql, $connect);
if ($query) echo "Successed!";
else echo "Failed!";
?>

The difference between mysql_db_query () and mysql_query () is that the former can select database databases without using mysql_select_db (), while the SQL statement is executed while the database is selected.