A database holds one or multiple tables.
Create a Database
The CREATE DATABASE statement is used to create a database in MySQL.
Syntax
| CREATE DATABASE database_name |
To get PHP to execute the statement above we must use the mysql_query() function. This function is used to send a query or command to a MySQL connection.
Example
The following example creates a database called “my_db”:
| <?php $con = mysql_connect(“localhost”,”peter”,”abc123″); if (!$con) { die(‘Could not connect: ‘ . mysql_error()); } if (mysql_query(“CREATE DATABASE my_db”,$con)) { echo “Database created”; } else { echo “Error creating database: ” . mysql_error(); } mysql_close($con); ?> |
Create a Table
The CREATE TABLE statement is used to create a table in MySQL.
Syntax
| CREATE TABLE table_name(column_name1 data_type,column_name2 data_type,column_name3 data_type,….) |
We must add the CREATE TABLE statement to the mysql_query() function to execute the command.
Example
The following example creates a table named “Persons”, with three columns. The column names will be “FirstName”, “LastName” and “Age”:
| <?php $con = mysql_connect(“localhost”,”peter”,”abc123″); if (!$con) { die(‘Could not connect: ‘ . mysql_error()); } // Create database if (mysql_query(“CREATE DATABASE my_db”,$con)) { echo “Database created”; } else { echo “Error creating database: ” . mysql_error(); } // Create table mysql_select_db(“my_db”, $con); $sql = “CREATE TABLE Persons(FirstName varchar(15),LastName varchar(15),Age int)”; // Execute query mysql_query($sql,$con); mysql_close($con); ?> |
Important: A database must be selected before a table can be created. The database is selected with the mysql_select_db() function.
Note: When you create a database field of type varchar, you must specify the maximum length of the field, e.g. varchar(15).
The data type specifies what type of data the column can hold.
Primary Keys and Auto Increment Fields
Each table should have a primary key field.
A primary key is used to uniquely identify the rows in a table. Each primary key value must be unique within the table. Furthermore, the primary key field cannot be null because the database engine requires a value to locate the record.
The following example sets the personID field as the primary key field. The primary key field is often an ID number, and is often used with the AUTO_INCREMENT setting. AUTO_INCREMENT automatically increases the value of the field by 1 each time a new record is added. To ensure that the primary key field cannot be null, we must add the NOT NULL setting to the field.
Example
| $sql = “CREATE TABLE Persons (personID int NOT NULL AUTO_INCREMENT, PRIMARY KEY(personID), FirstName varchar(15), LastName varchar(15), Age int)”; mysql_query($sql,$con); |