Report error while performing UPDATE with SQL

Question

I have a project, in which the administrator can change registered data of tables, but if the query is executed, but no change occurs, I would like to return a message or error, here’s what I have so far:

$altera = "UPDATE z SET y= a WHERE x= x";
$select = mysql_query($altera);
if($select){
   mensagem de sucesso
}else{
   mensagem de erro
}

The variables and things like that are not important, what matters is the if there at the end, which, I think, if the variable occurs, will do what is inside the brackets, if it doesn’t occur, will show error message, but this doesn’t work, and I don’t know who else to turn to.

Answer 1

I use it this way with Firebird:

if ($query){
    echo "Tudo OK";
}

if (ibase_errmsg()){
    echo "Erro técnico: ".ibase_errmsg();
}

You can do with the function mysql_error().

mysql_error - Returns the text of the previous Mysql operation error message

Example with Mysql with your problem:

  $altera = "UPDATE z SET y= a WHERE x= x";
  $select = mysql_query($altera);

  if($select){
      // tratativa caso for bem-sucedido
  } 

  if (mysql_error()){
      // tratativa caso for mal-sucedido
  }

Observing:

Mysql functions that start with mysql_* are obsolete and will be discontinued from PHP 7, consider using mysqli_*.

References:

http://php.net/manual/en/function.mysql-error.php

http://php.net/manual/en/function.ibase-errmsg.php

Answer 2

This can be done using the function mysql_affected_rows which returns the number of lines actually affected in the last query using the UPDATE.

$altera = "UPDATE z SET y= a WHERE x= x";
$select = mysql_query($altera);
   if($select){
      if(mysql_affected_rows() > 0){
        print "foram atualizadas (". mysql_affected_rows() .") linhas";
      } else {
        print "consulta efetuada, mas nenhuma linha modificada";
      }
   }else{ 
      die("Erro: " . mysql_error());
   }

Regardless of what you want, both the if($select) or if(!$select) as a mysql_errno() would have the same impact if it were to verify whether such a query was executed, and if($select) checks if the returned value has been executed (true) or not (false), mysql_errno() returns the error number of the last operation, if it has failed, the same way it does the mysql_error() but this returns the error as a numerical value.

For the compatibility problem with even lower versions, there is the function mysql_numrows() (also discontinued).

Warning This Extension was deprecated in PHP 5.5.0, and it was Removed in PHP 7.0.0. Instead, the Mysqli or Pdo_mysql Extension should be used. See also Mysql: Choosing an API guide and Related FAQ for more information.

In the documentation in Portuguese this warning is omitted, or why I do not know, but it practically says that functions like mysql_* are obsolete, that is, the use of these functions is discouraged, from the PHP >= 5.5.0 and were completely removed from the PHP >= 7.0.0.

Alternatively, there are the following extensions:

• Mysqli (Mysql Improved)
• PDO (PHP Data Objects)

Some references:

• Why should we not use mysql type functions_*?
• What is the right way to connect to the Mysqli database
• Mysqli vs PDO - which is the most recommended to use?
• mysql_errno
• mysql_error
• mysql_affected_rows