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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.
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It allows any condition to be specified.
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It allows for the specification of multiple conditions through using an AND or OR operator.
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Case sensitivity only applies to statements using LIKE comparisons.
The WHERE clause permits the use of the following operators −
| Operator |
|---|
| = != |
| > < |
| >= <= |
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
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