我的PDO mysql查询有什么问题[重复]

Question

This question already has an answer here:

• Invalid Parameter Number. Parameter not defined 1 answer

Here is my code

$sql3= "select * 
        from comments 
        where status=:status  
        limit=:limit 
        offset=:offset 
        order by time desc";
$query3= $pdo->prepare($sql3);
$query3->bindValue(":status",'n');
$query3->bindValue(":limit",$per_page);
$query3->bindValue(":offest",$offset);
$query3->execute();
$comments=$query3->fetchall();

Here comments is my table name status and time is two column in my table . Whenever I run this code , It shows a warning

Warning: PDOStatement::execute(): SQLSTATE[HY093]: Invalid parameter number: parameter was not defined in E:\XAMPP\htdocs\parlament\user\logged_in_area.php

What does this mean ?

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Answer 1

The answer depends of what are limit and offset.

If they're columns names...

• You can't use these reserved keywords for column names without backticks
• You need to add a AND / OR operator between your lines

$sql3= "select * 
        from comments 
        where status=:status  
        and `limit`=:limit 
        and `offset`=:offset 
        order by time desc";
$query3= $pdo->prepare($sql3);
$query3->bindValue(":status", 'n');
$query3->bindValue(":limit", $per_page);
$query3->bindValue(":offest", $offset);
$query3->execute();
$comments=$query3->fetchall();

If they're keywords...

• The syntax is LIMIT <n>, not LIMIT = <n> (same for OFFSET)
• It better to specify their type with PDO::PARAM_INT (same for OFFSET)
• ORDER BY must be added before LIMIT and OFFSET

$sql3= "select * 
        from comments 
        where status=:status 
        order by time desc 
        limit :limit 
        offset :offset";
$query3= $pdo->prepare($sql3);
$query3->bindValue(":status", 'n');
$query3->bindValue(":limit", (int)$per_page, PDO::PARAM_INT);
$query3->bindValue(":offset", (int)$offset, PDO::PARAM_INT);
$query3->execute();
$comments=$query3->fetchall();