SELECT statements retrieve selected rows. They can include UNION statements, an ordering clause, a LIMIT clause, a WHERE clause, a GROUP BY…HAVING clause, and subqueries.
Review the following general syntax:
SELECT field, field2,... FROM table_name, table_name2,... WHERE...
A SELECT statement provides multiple options for specifying the table used:
- database_name.table_name
- table_name.column_name
- database_name.table_name.column_name
All select statements must contain one or more select expressions. Select expressions consist of one of the following options:
- A column name.
- An expression employing operators and functions.
- The specification “table_name.*” to select all columns within the given table.
- The character “*” to select all columns from all tables specified in the FROM clause.
The command prompt or a PHP script can be employed in executing a select statement.
The Command Prompt
At the command prompt, execute statements as follows:
root@host# mysql -u root -p password; Enter password:******* mysql> use PRODUCTS; Database changed mysql> SELECT * from products_tbl +-------------+---------------+ | ID_number | Nomenclature | +-------------+---------------+ | 12345 | Orbitron 4000 | +-------------+---------------+
PHP Select Script
Employ the same SELECT statement(s) within a PHP function to perform the operation.
You will use the mysql_query() function once again. Review an example given below:
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn )
{
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT product_id, product_name,
product_manufacturer, ship_date
FROM products_tbl';
mysql_select_db('PRODUCTS');
$retval = mysql_query( $sql, $conn );
if(! $retval )
{
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC))
{
echo "Product ID :{$row['product_id']} <br> ".
"Name: {$row['product_name']} <br> ".
"Manufacturer: {$row['product_manufacturer']} <br> ".
"Ship Date : {$row['ship_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>
On successful data retrieval, you will see the following output:
Product ID: 12345 Nomenclature: Orbitron 4000 Manufacturer: XYZ Corp Ship Date: 01/01/17 ---------------------------------------------- Product ID: 12346 Nomenclature: Orbitron 3000 Manufacturer: XYZ Corp Ship Date: 01/02/17 ---------------------------------------------- mysql> Fetched data successfully
Best practices suggest releasing cursor memory after every SELECT statement. PHP provides the mysql_free_result() function for this purpose. Review its use as shown below:
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn )
{
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT product_id, product_name,
product_manufacturer, ship_date
FROM products_tbl';
mysql_select_db('PRODUCTS');
$retval = mysql_query( $sql, $conn );
if(! $retval )
{
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_NUM))
{
echo "Product ID :{$row[0]} <br> ".
"Name: {$row[1]} <br> ".
"Manufacturer: {$row[2]} <br> ".
"Ship Date : {$row[3]} <br> ".
"--------------------------------<br>";
}
mysql_free_result($retval);
echo "Fetched data successfully\n";
mysql_close($conn);
?>