WHERE clauses filter various statements such as SELECT, UPDATE, DELETE, and INSERT. They present criteria used to specify action. They typically appear after a table name in a statement, and their condition follows. The WHERE clause essentially functions like an if statement.

Review the general syntax of WHERE clause given below −

[COMMAND] field,field2,... FROM table_name,table_name2,... WHERE [CONDITION]

Note the following qualities of the WHERE clause −

• It is optional.

• It allows any condition to be specified.

• It allows for the specification of multiple conditions through using an AND or OR operator.

• Case sensitivity only applies to statements using LIKE comparisons.

The WHERE clause permits the use of the following operators −

WHERE clauses can be utilized at the command prompt or within a PHP script.

The Command Prompt

At the command prompt, simply use a standard command −

root@host# mysql -u root -p password;
Enter password:*******
mysql> use PRODUCTS;
Database changed
mysql> SELECT * from products_tbl WHERE product_manufacturer = ''XYZ Corp
+-------------+----------------+----------------------+
| ID_number   | Nomenclature   | product_manufacturer |
+-------------+----------------+----------------------+
| 12345       | Orbitron 4000  | XYZ Corp             |
+-------------+----------------+----------------------+
| 12346       | Orbitron 3000  | XYZ Corp             |
+-------------+----------------+----------------------+
| 12347       | Orbitron 1000  | XYZ Corp             |
+-------------+----------------+----------------------+

Review an example using the AND condition −

SELECT *
FROM products_tbl
WHERE product_name = ''Bun Janshu 3000
AND product_id <= 344;

This example combines both AND and OR conditions

SELECT *
FROM products_tbl
WHERE (product_name = ''Bun Janshu 3000'' AND product_id < 344)
OR (product_name = ''Bun Janshu 3000'');

PHP Scripts Using Where Clause

Employ the mysql_query() function in operations using a WHERE clause −

<?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
      WHERE product_manufacturer = "XYZ Corp"
   
   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 successfullyn";
   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
----------------------------------------------
Product ID: 12347
Nomenclature: Orbitron 1000
Manufacturer: XYZ Corp
Ship Date: 01/02/17
----------------------------------------------
mysql> Fetched data successfully