MariaDB selects the query

In this chapter, we'll learn how to select data from a table.

The SELECT statement retrieves the selected row. T hey can include UNION statements, sort clauses, LIMIT clauses, WHERE clauses, GROUP BY ... H AVING clauses and sub-queries.

See the following general syntax -

SELECT field, field2,... FROM table_name, table_name2,... WHERE...

Select statements provide several options to specify which tables to use -

• database_name.table_name

• table_name.column_name

• database_name.table_name.column_name

All select statements must contain one or more select expressions. T he selection expression consists of one of the following options -

• The column name.

• Expressions that use operators and functions.

• The specification "table_name ."" to select all the columns in a given table.

• The character """

You can use command prompts or PHP scripts when executing select statements.

Command prompt

Under the command prompt, execute the following statement:

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 selection script

Use the same SELECT statement in the PHP function to perform the operation. Y ou will use the mysql_query() function again. S ee the 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
";
   mysql_close($conn);
?>

In a 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 recommend freeing cursor memory after each SELECT statement. P HP provides a mysql_free_result() function for this purpose. R eview its use as follows -

<?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($retval);
   echo "Fetched data successfully
";
   mysql_close($conn);
?>