What is WHERE query in Mysqli?

We have seen SQL SELECT command to fetch data from MySQLi table. We can use a conditional clause called WHERE clause to filter out results. Using WHERE clause, we can specify a selection criteria to select required records from a table.

Syntax

Here is generic SQL syntax of SELECT command with WHERE clause to fetch data from MySQLi table −

SELECT field1, field2,...fieldN table_name1, table_name2...
[WHERE condition1 [AND [OR]] condition2.....

• You can use one or more tables separated by comma to include various conditions using a WHERE clause, but WHERE clause is an optional part of SELECT command.
• You can specify any condition using WHERE clause.
• You can specify more than one conditions using AND or OR operators.
• A WHERE clause can be used along with DELETE or UPDATE SQL command also to specify a condition.

The WHERE clause works like an if condition in any programming language. This clause is used to compare given value with the field value available in MySQLi table. If given value from outside is equal to the available field value in MySQLi table, then it returns that row.

Here is the list of operators, which can be used with WHERE clause.

Assume field A holds 10 and field B holds 20, then −

Operator	Description	Example
=	Checks if the values of two operands are equal or not, if yes then condition becomes true.	(A = B) is not true.
!=	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

The WHERE clause is very useful when you want to fetch selected rows from a table, especially when you use MySQLi Join. Joins are discussed in another chapter.

It is a common practice to search records using Primary Key to make search fast.

If given condition does not match any record in the table, then query would not return any row.

Fetching Data from Command Prompt

This will use SQL SELECT command with WHERE clause to fetch selected data from MySQLi table tutorials_inf.

Example

Following example will return all the records from tutorials_inf table for which name is sai −

root@host# mysql -u root -p password;
Enter password:*******

mysql> use TUTORIALS;
Database changed

mysql>SELECT * from tutorials_inf where name = 'sai';
+----+------+
| id | name |
+----+------+
|  1 | SAI  |
+----+------+
1 row in set (0.00 sec)

mysql>

Unless performing a LIKE comparison on a string, the comparison is not case sensitive. You can make your search case sensitive using BINARY keyword as follows −

root@host# mysql -u root -p password;
Enter password:*******

mysql> use TUTORIALS;
Database changed

mysql> SELECT * from tutorials_inf \WHERE BINARY name = 'sai';
Empty set (0.02 sec)

mysql>

Fetching Data Using PHP Script:

You can use same SQL SELECT command with WHERE CLAUSE into PHP function mysqli_query().

Example

Following example will return all the records from tutorials_inf table for which name is sai −

<?php
   $dbhost = 'localhost:3306';
   $dbuser = 'root';
   $dbpass = '';
   $dbname = 'TUTORIALS';
   $conn = mysqli_connect($dbhost, $dbuser, $dbpass,$dbname);
   
   if(! $conn ) {
      die('Could not connect: ' . mysqli_error());
   }
   echo 'Connected successfully<br>';
   $sql = 'SELECT * from tutorials_inf where name="sai"';
   $result = mysqli_query($conn, $sql);

   if (mysqli_num_rows($result) > 0) {
      while($row = mysqli_fetch_assoc($result)) {
         echo "Name: " . $row["name"]. "<br>";
      }
   } else {
      echo "0 results";
   }
   mysqli_close($conn);
?>

The sample output should be like this −

Connected successfully
Name: SAI