php MySQL Create Database Create database

MySQL Create Database Create database

Create database

CREATE DATABASE syntax is used to create a database.

Syntax:

CREATE DATABASE db_name

In the PHP MySQL function library, the mysql_query() function is used to send and execute SQL statements to MySQL. For more detailed information about the mysql_query() function, please refer to "MySQL mysql_query".

Create a database named testdb:

<?php
$conn = @mysql_connect("localhost","root","root1234");
if (!$conn){
    die("连接数据库失败：" . mysql_error());
}
if (@mysql_query("CREATE DATABASE testdb",$conn)){
    echo "创建数据库成功！";
} else {
    echo "创建数据库失败：" . mysql_error();
}
?>

Tips

Creating a database requires corresponding user permissions, such as root user

In the actual virtual host space, the virtual host provider has usually created the corresponding database. Therefore, the above example may not run successfully

Select a database

When you want to perform operations on a database or table, you need to select a database. mysql_select_db() is used to select a database. The function returns true if successful and false if failed.

Syntax:

bool mysql_select_db(string db_name [, resource connection])

Parameter description:

Parameter description

db_name The database name to be selected

connection Optional, connect the database identification resource, use if not specified The previous connection

For specific usage, see the example of creating a data table below.

Create a data table

Create a data table The SQL syntax is as follows:

CREATE TABLE table_name
(
    column1 data_type,
    column2 data_type,
    column3 data_type,
    .......
)

In the above syntax, column is the field name, followed by the data type.

Create a table named user:

<?php
$conn = @mysql_connect("localhost","root","root1234");
if (!$conn){
    die("连接数据库失败：" . mysql_error());
}
//选择数据库
mysql_select_db("test", $conn);
//创建数据表 SQL
$sql = "CREATE TABLE user (
uid mediumint(8),
username varchar(20),
password char(32),
email varchar(40),
regdate int(10)
)";
if(!mysql_query($sql,$conn)){
    echo "创建数据表失败：". mysql_error();
} else {
    echo "创建数据表成功！";
}
?>

In this example, it is divided into 3 execution steps:

Create a database link

Use the mysql_select_db() function to select the database that holds the table

Use mysql_query() The function creates a data table

The table created in this example has 4 fields and the corresponding data object type is specified.

Principles of table building

Generally speaking, there are the following precautions when creating a data table:

Correspondence between original record data and table

Table name and field name should follow the naming syntax and should have clear meaning

Specify the data type of the field

Specify other attributes of the field, such as whether it is non-null, whether it has a default value, etc.

Define table attributes such as primary and foreign keys, constraints, indexes, etc.

The relationship with other tables

Limited to the length and to control the difficulty of the tutorial , will not be discussed too much here.

Tips

This table creation example is only to demonstrate the basic table creation syntax and is not complete. In actual production, we also need to specify more attributes for tables and fields.