prepare（）输出bool false，语句对我来说是正确的[重复]

Question

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• mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc… expects parameter 1 to be resource or result 32 answers

I have a function that executes a prepared statement. I've pinpointed the problem to the SQL code by wrapping the prepare() line with an exception catcher, but I can't figure out what is wrong with it.

This is the function

    function update_table($column, $value, $conn, $email) {
        require "config.php";
        $stmtupdate = $conn->prepare("UPDATE $table SET ? = ? WHERE email = ?");
        $stmtupdate->bind_param("sis", $column, $value, $email);
        $stmtupdate->execute();
        $stmtupdate->close();
    }

This is one of the function calls

update_table("failedCount", 0, $conn, $email);

Error printed to the page

Fatal error: Uncaught Error: Call to a member function bind_param() on boolean in /var/www/html/usenergy/login.php:125 Stack trace: #0 /var/www/html/usenergy/login.php(218): update_table('failedCount', 0, Object(mysqli), 'testmail@test...') #1 {main} thrown in /var/www/html/usenergy/login.php on line 125

column is a string that defines the column name where $value will be set to ($value is integer).

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Answer 1

You have this:

$stmtupdate = $conn->prepare("UPDATE $table SET ? = ? WHERE email = ?");
$stmtupdate->bind_param("sis", $column, $value, $email);

This results in this SQL:

UPDATE $table
SET @var1 = @var2 WHERE email = @var3

substituted for example with

UPDATE $table
SET 'column' = 123 WHERE email = 'something'

But you want something like

UPDATE mytable
SET mycolumn = 123 WHERE email = 'something'

So there are two mistakes: You want a table name, not $table. And you want a column name, not a string bind variable value.

Use string concatenation:

$stmtupdate = $conn->prepare("UPDATE ".$table." SET ".$column." = ? WHERE email = ?");
$stmtupdate->bind_param("is", $value, $email);

(I hope I'm not mistaken. It's been some time since I used PHP with SQL.)