PHP & MySql 检查表是否为空
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PHP & MySql check if table is empty
提问by user517593
I'm a bit of a noob- and I'm having a hard time...
我有点菜鸟 - 我很难过......
I need a bit of of code that searches a db table to find the row that matches the $id variable. There's a field in that table 'description' that I need to grab. If it's null, I need to show one message, if not another. Here's the code I have (I know I need to add the mysqli escape string, just doing this real quick from memory):
我需要一些代码来搜索 db 表以找到与 $id 变量匹配的行。我需要获取该表“描述”中的一个字段。如果它为空，我需要显示一条消息，如果不是另一条。这是我的代码（我知道我需要添加 mysqli 转义字符串，只需从内存中快速执行此操作）：
$query = "SELECT description FROM posts WHERE id = $id";
$result = mysqli_query($dbc, $query);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC) ;
if(!$row){
echo "<p>'No description'</p>";
} else {
echo '<p>' . $row['description'] . '</p>';
}
回答by Josh
mysqli_fetch_arraywill fetch a row regardless of if the columns in that row are null. You want to be checking if $row['description']is set instead of if $rowis set:
mysqli_fetch_array无论该行中的列是否为空，都将获取一行。您想检查是否$row['description']已设置而不是是否$row已设置：
$query = "SELECT description FROM posts WHERE id = $id";
$result = mysqli_query($dbc, $query);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
if(isset($row['description'])) {
echo "<p>No description</p>";
} else {
echo '<p>' . $row['description'] . '</p>';
}
EDIT:Or, as an alternative, you can not fetch rows from the database where description is NULL:
编辑：或者，作为替代方案，您无法从描述为 NULL 的数据库中获取行：
$query = "SELECT description FROM posts WHERE id = $id AND description IS NOT NULL LIMIT 1";
$result = mysqli_query($dbc, $query);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
if(! $row) {
echo "<p>No description</p>";
} else {
echo '<p>' . $row['description'] . '</p>';
}
Nowyou'd check to see if you were able to grab a row or not.
现在你要检查你是否能够抓住一行。
回答by Marc
The !$rowwill only occur if no record is found. If the field description is really null, you have to check it this way:
在!$row如果没有记录被发现时才会发生。如果字段描述真的是null，你必须这样检查：
if(is_null($row['description'])){
but I recommend you to check if the value is empty (or 0 or null):
但我建议您检查该值是否为空（或 0 或 null）：
if(empty($row['description'])){
回答by Sarfraz
BTW, you can do the check from within your query using COALESCE:
顺便说一句，您可以使用COALESCE以下方法从查询中进行检查：
$query = "SELECT COALESCE(description, 'No description') FROM posts WHERE id = $id";
$result = mysqli_query($dbc, $query);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC) ;
echo $row['description'];
This way, when there is a value for the descriptionfield, it will be shown otherwise No descriptionwill be output. So that way, you can do away with the ifcondition of PHP.
这样，当该description字段有值时，它将被显示，否则No description将被输出。这样，您就可以摆脱ifPHP的条件。
回答by Michael B
How about:
怎么样：
SELECT COUNT(*) FROM table WHERE `description` IS NOT NULL
