我怎么知道我的mysql_query更新实际上没有更新任何内容？

Question

I am doing an update to a table for a row that may not exist. If it doesn't exist, I need to do an insert. I was initially planning on knowing that I needed to do an insert based on a negative return value from the update statement, but it isn't returning anything negative.

How can I know that the update didn't do anything? Do another query seeing if anything is there? Or maybe a query before?

Thanks!

Answer 1

Use http://php.net/manual/en/function.mysql-affected-rows.php

Get the number of affected rows by the last INSERT, UPDATE, REPLACE or DELETE query associated with link_identifier.

<?php
$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {
    die('Could not connect: ' . mysql_error());
}
mysql_select_db('mydb');

/* this should return the correct numbers of deleted records */
mysql_query('DELETE FROM mytable WHERE id < 10');
printf("Records deleted: %d\n", mysql_affected_rows());

/* with a where clause that is never true, it should return 0 */
mysql_query('DELETE FROM mytable WHERE 0');
printf("Records deleted: %d\n", mysql_affected_rows());
?>

If you're using mysqli instead of mysql ( mysql was deprecated a long time ago), it's mysqli_affected_rows .

Answer 2

Simply mysql_affected_rows method is the way to find out the change in table in both case if table exist or not. However, for optimized code better to check first for table existence like:

$status = mysql_query("select * from table_name");
if($status==false){
   echo "table don't exists";
}
else{
  //do your stuff here
}