Describe in detail what data types will be returned by php querying the database

In the process of using PHP to query the database, we often need to understand the data type returned by the query results, so that we can better process and use the data. PHP can use various methods and functions to query the database, but no matter which method is used, the query results will return certain data types. This article will give you a detailed introduction to the data types returned by PHP querying the database.

1. Array type

In PHP, one of the most common data types is the array. When we query the database using a SQL statement similar to "SELECT * FROM table", the query results will be encapsulated into an array. Each element in the array represents a record in the database, where the key name of each element corresponds to the field name, and the corresponding key value is the value corresponding to the field. For example:

$conn = mysqli_connect($host, $user, $password, $database);
$result = mysqli_query($conn, "SELECT * FROM table");
$rows = array();
while($row = mysqli_fetch_assoc($result)) {
    $rows[] = $row;
}
print_r($rows);

The above code encapsulates the query results into a two-dimensional array, where each one-dimensional array represents a record in the database. The key name of the array is the same as the field name in the database, and the corresponding key value is the value of this field.

2. Object type

In addition to array types, query results can also be encapsulated as object types. The main benefit of using object types is that you can get and set class properties through object accessors. For example:

$conn = mysqli_connect($host, $user, $password, $database);
class Record {
    public $field1;
    public $field2;
}
$result = mysqli_query($conn, "SELECT * FROM table");
$rows = array();
while($row = mysqli_fetch_object($result, Record::class)) {
    $rows[] = $row;
}
print_r($rows);

The above code encapsulates the query result into a Record class object. The attribute name of the object is the same as the field name in the database, and the corresponding attribute value is the value of the field.

3. Integer and floating point types

When we use a SQL statement similar to "SELECT COUNT(*) FROM table" to query the database , the query result will return an integer value, which represents the number of records matching the query conditions. Similarly, when we use aggregate functions such as SUM, AVG, etc., the query result will also return a floating point value, which represents the statistical information of the query results. For example:

$conn = mysqli_connect($host, $user, $password, $database);
$result = mysqli_query($conn, "SELECT COUNT(*) FROM table");
$count = mysqli_fetch_row($result);
echo "Total rows: " . $count[0];

The above code encapsulates the query result into an integer value, which represents the number of records matching the query conditions.

4. Boolean

When we query the database using a SQL statement similar to "SELECT field1 FROM table WHERE field2 = 'value'", The query result will return a Boolean value, which indicates whether the specified value value exists in field field2. For example:

$conn = mysqli_connect($host, $user, $password, $database);
$result = mysqli_query($conn, "SELECT field1 FROM table WHERE field2 = 'value'");
if(mysqli_num_rows($result) > 0) {
    echo "Value exists.";
} else {
    echo "Value does not exist.";
}

The above code encapsulates the query result into a Boolean value, which indicates whether the specified value value exists in field field2.

Summary:

The above are several data types returned by PHP query database, including array type, object type, integer type, floating point type and Boolean type. To flexibly use the data types in the query results, you can perform data conversion and type judgment as needed.

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