Summarize several ways to query whether a field has a value in PHP

In PHP development, it is often necessary to query whether a certain field has a value, so that the next step can be performed based on whether there is a value. This article will introduce several ways to query whether a field has a value in PHP.

1. Use the isset function

In PHP, you can use the isset function to determine whether a variable has been defined and the value is not null. Combined with database operations, you can determine whether a field has a value by querying whether it is empty.

Sample code:

$query = "SELECT field FROM table WHERE id = 1";
$result = mysqli_query($conn, $query);
$row = mysqli_fetch_assoc($result);
if(isset($row['field'])){
    //字段有值
} else {
    //字段为空
}

2. Use the empty function

The empty function can be used to determine whether a variable is empty, but it should be noted that, empty not only determines whether the variable is null, but also determines whether many other conditions are empty, such as empty string, 0, false, etc.

Sample code:

$query = "SELECT field FROM table WHERE id = 1";
$result = mysqli_query($conn, $query);
$row = mysqli_fetch_assoc($result);
if(!empty($row['field'])){
    //字段有值
} else {
    //字段为空
}

3. Use the is_null function

The is_null function can be used to determine whether a variable is null. Because is_null only determines whether a variable is null, it is not suitable for determining whether a string or other non-null type value is empty.

Sample code:

$query = "SELECT field FROM table WHERE id = 1";
$result = mysqli_query($conn, $query);
$row = mysqli_fetch_assoc($result);
if(!is_null($row['field'])){
    //字段有值
} else {
    //字段为空
}

4. Use the mysqli_num_rows function

Use the mysqli_num_rows function to obtain the number of rows in the query result set. If the number of rows is greater than 0, it means that the field has a value.

Sample code:

$query = "SELECT field FROM table WHERE id = 1";
$result = mysqli_query($conn, $query);
if(mysqli_num_rows($result) > 0){
    //字段有值
} else {
    //字段为空
}

The above are several ways to query whether a field has a value in PHP. According to personal habits or needs, you can choose one or more of these methods to determine whether the fields in the database query results have values.

The above is the detailed content of Summarize several ways to query whether a field has a value in PHP. For more information, please follow other related articles on the PHP Chinese website!