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@mysql_query  and mysql_query whats the difference?

Posted on 2006-07-06
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Last Modified: 2013-12-12
hi

I have 2 scripts that do very similar things,  one has this line
  $ret = @mysql_query($sql);
and the other
  $ret = mysql_query($sql);

the SQL is for all puropses the same.  want to know what the @ mark means.  

michael
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Question by:ussher
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Expert Comment

by:Guy Hengel [angelIII / a3]
Comment Utility
@ supresses that the page prints out a error message, so you can handle it (using mysql_error() )

@ can be used for ALL functions, not only mysql...
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Accepted Solution

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RQuadling earned 100 total points
Comment Utility
@ means suppress any non fatal errors.

In fact it may even suppress them!

If using @, normally the next line of code will be determining if the result is a failure (in context with the function).

e.g. (from my own DB class)

      private function MakeDBConnection($objKrypt)
            {
            $resResult = @odbc_pconnect($this->DSN, $this->sUser, $objKrypt->Dekrypt($this->sPassword));
            if ($resResult === False)
                  {
                  throw new class_DB_Exception(
                        class_DB_Exception::DB_ERROR_SERVER_CONNECT,
                        array(
                              $this->sServer
                              )
                        );
                  }
            return $resResult;
            }

As you can see the odbc_pconnect() function can be false. Normally this will output a message also. By using @ the message is not reported and I can still continue testing the result.
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Author Comment

by:ussher
Comment Utility
so if error reporting is turned off at the server level both statements are exactly the same?
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Expert Comment

by:RQuadling
Comment Utility
I think so. But just because you can't see the error, doesn't mean the function hasn't worked!

Error suppression is not a route to take if you want to have a stable app.

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Expert Comment

by:RQuadling
Comment Utility
Too many negatives!

No error message does not mean the function HAS worked!
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Author Comment

by:ussher
Comment Utility
ok thanks.  for now i will remove it and see if there are any errors but once it gets to production i dont want clients seeing errors.

im a bit clearer at what im looking at now.

cheers
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Expert Comment

by:RQuadling
Comment Utility
No.

Wrong way round.

Keep it in and add a test to see if the returned value is the error value. In mysql_query()'s case that would be false.

$ret = @mysql_query($sql);
if (False === $ref)
 {
 // Then something went wrong. Depending upon the statement, you may be able to handle the error or not.
 }
else
 {
 // The query was executed successfully. I would now be checking the mysql_affected_rows() (for update/insert/delete) or mysql_num_rows() (for select) to make sure the query performed as I expected it to.
 }

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by:ussher
Comment Utility
ok thanks.  Ill get it printing something

if (False === $ref) why 3 equals signs?  I have seen == before and know what that menas but never 3.  does it have a different meaning?

michael
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Author Comment

by:ussher
Comment Utility
sorry. got it
 === identical operator

RTFM

thanks for your help

michael
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Expert Comment

by:RQuadling
Comment Utility
PHP is loosely typed.

This means that

0 == "0" == False

zero equals in value the string "0" equals in value False.

BUT === means equal in value AND type.

0 !== "0" !== False

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Expert Comment

by:RQuadling
Comment Utility
And the reason why you use False !== is that you want to ONLY test that the function returned a boolean True.

e.g.

strpos('ABC', 'A')

The answer is 0

But

<?php
if (False == strpos('ABC', 'A'))
 {
 echo 'A not present';
 }
?>

is clearly wrong.


<?php
if (False === strpos('ABC', 'A'))
 {
 echo 'A not present';
 }
?>

is the right way.

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Author Comment

by:ussher
Comment Utility
awesome.

im now one step closer to enlightenment. (had to get the manual out and looked up strpos)

thanks

michael

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