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With the rise of the Internet, web development has become more and more popular. In web development, an important task is to deal with the database. In php, MySQL is one of the most popular database services. PHP provides very convenient methods to connect and operate MySQL database, such as executing SQL query statements.
In this article, we will discuss how to write sql query statements. These queries can be used to retrieve data stored in the database, they can be single or multiple rows, or they can use a series of conditions and sorting to limit the data returned.
First, we need to connect to the database. In PHP, we can use the mysqli_connect() function to establish a connection to the MySQL database. This function requires the host name, user name, password and database name as parameters. After the connection is successful, we can use the mysqli_query() function to execute the sql query statement.
The following are some common sql query statements, and we will discuss how to use them in php one by one.
The SELECT statement is the most basic SQL statement used to retrieve data from one or more tables. In php, we can use the mysqli_fetch_array() function to retrieve the data returned by the SELECT query. This function will return a row of query results as an array, and it returns false after all rows have been read.
The following is a sample SELECT statement:
SELECT * FROM users;
In php, you can use the following code to execute a SELECT query and return its results:
$conn = mysqli_connect("localhost", "username", "password", "database_name");
$result = mysqli_query($conn, "SELECT * FROM users");
while($row = mysqli_fetch_array($result)) {
echo $row['id']." ".$row['name']." ".$row['email']."
";
}
The WHERE statement is used to filter the results of the SELECT statement and only return rows that meet the conditions. In php, we can use the WHERE statement as part of the SELECT query.
The following is a sample WHERE statement:
SELECT * FROM users WHERE name='Grace';
In php, you can use the following code to perform a WHERE query and return its results:
$conn = mysqli_connect("localhost", "username", "password", "database_name");
$result = mysqli_query($conn, "SELECT * FROM users WHERE name='Grace'");
while($row = mysqli_fetch_array($result)) {
echo $row['id']." ".$row['name']." ".$row['email']."
";
}
ORDER BY statement is used to sort the results of a SELECT statement by a specified column. In php, we can use the ORDER BY statement as part of the SELECT query.
The following is a sample ORDER BY statement:
SELECT * FROM users ORDER BY name ASC;
In php, you can use the following code to perform an ORDER BY query and return its results:
$conn = mysqli_connect("localhost", "username", "password", "database_name");
$result = mysqli_query($conn, "SELECT * FROM users ORDER BY name ASC");
while($row = mysqli_fetch_array($result)) {
echo $row['id']." ".$row['name']." ".$row['email']."
";
}
The LIMIT statement is used to limit the number of rows returned by the SELECT statement. In php, we can use the LIMIT statement as part of the SELECT query.
The following is a sample LIMIT statement:
SELECT * FROM users LIMIT 5;
In php, you can use the following code to execute a LIMIT query and return its results:
$conn = mysqli_connect("localhost", "username", "password", "database_name");
$result = mysqli_query($conn, "SELECT * FROM users LIMIT 5");
while($row = mysqli_fetch_array($result)) {
echo $row['id']." ".$row['name']." ".$row['email']."
";
}
Summary
The above are some common sql query statements in php and how to use them. You can tailor these queries to your needs to return the data you need. Please note that each query needs to be used with the correct database connection.
At the same time, please be aware of the issue of SQL injection attacks. Never trust user-supplied data and always use parameterized queries to prevent SQL injection attacks.
I hope this article can help you better understand how to write sql query statements in php, and help you better use the MySQL database.
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