php MySQL Create Database Create database
Java Code
MySQL Create Database Create Database
Create Database
CREATE DATABASE syntax is used to create a database.
Syntax:
CREATE DATABASE db_name
PHP In the 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 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. If successful, the function returns true, if failed, it returns false.
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, If not specified, use Previous link
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 accommodates the table
Use mysql_query() Function creates data table
The table created in this example has 4 fields and the corresponding data object type is specified.
Principles of table creation
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-empty, whether it has a default value, etc.
Define table attributes such as primary and foreign keys, constraints, indexes, etc.
Relationships with other tables
Limited to space 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.
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