Simulating an atomic operation for application locks using mysql.
$link = mysql_connect('localhost', 'user', 'pass');
if (!$link) {
die('Not connected : ' . mysql_error());
}
// make foo the current db
$db_selected = mysql_select_db('foo', $link);
if (!$db_selected) {
die ('Can\'t use foo : ' . mysql_error());
}
$q = "update `table` set `LOCK`='F' where `ID`='1'";
$lock = mysql_affected_rows();
If we assume
NOT LOCKED = "" (empty string)
LOCKED = 'F'
then if the column LOCK had a value other than F (normally should be an empty string) the update statement sets it to F and set the affected rows to 1. Which mean than we got the lock.
If affected rows return 0 then the value of that column was already F and somebody else has the lock.
The secret lies in the following statement taken from the mysql manual:
"If you set a column to the value it currently has, MySQL notices this and does not update it."
Of course all this is possible if the all application processes agree on the locking algorithm.
mysql_query
(PHP 4, PHP 5)
mysql_query — Invia una query MySQL
Descrizione
mysql_query(string
$query, resource $identificativo_connessione = ?, int $modo_risultato = ?): resource
mysql_query() invia una query al database
attualmente attivo sul server associato all'identificativo di conmnessione
specificato. Se
identificativo_connessione non è specificato, viene considerata l'ultima
connessione aperta. Se nessuna connessione è aperta, la funzione prova
a stabilire una connessione come se mysql_connect() fosse
richiamata senza argomenti ed usa questa.
Il paramentro opzionale modo_risultato
può essere MYSQL_USE_RESULT e MYSQL_STORE_RESULT. Il valore
predefinito MYSQL_STORE_RESULT, così il risultato è bufferato.
Vedere anche mysql_unbuffered_query() per la
controparte di questo comportamento.
Nota:
La stringa della query non dovrebbe terminare con un punto e virgola.
Solo per le istruzioni SELECT, SHOW, EXPLAIN o DESCRIBE
mysql_query()
restituisce un identificativo di risorsa o false se la query non
è stata eseguita correttamente. Per altri tipi di istruzioni SQL,
mysql_query() restituisce true in caso di successo
e false in caso di errore. Un valore restituito diverso da false
indica che la query era lecita ed è stata eseguita dal
server. Questo non indica niente riguardo il numero di
righe coinvolte o restituite. è assolutamente possibile che una query
abbia successo ma che non coinvolga o restituisca nessuna riga.
La seguente query non è valida sintatticamente, quindi
mysql_query() fallisce e restituisce false:
Example #1 mysql_query()
<?php
$risultato = mysql_query("SELECT * WHERE 1=1")
or die("Query non valida: " . mysql_error());
?>
La seguente query non è semanticamente valida se
mia_colonna non è una colonna della tabella
mia_tabella, quindi mysql_query()
fallisce e retituisce false:
Example #2 mysql_query()
<?php
$risultato = mysql_query("SELECT mia_colonna FROM mia_tabella")
or die("Query non valida: " . mysql_error());
?>
mysql_query() fallisce e restituisce false
anche se non si hanno i permessi per accedere alle tabelle cui la query
fa riferimento.
Assumendo che la query abbia succeesso, si può richiamare mysql_num_rows() per scoprire quante righe sono state restituite da un'istruzione SELECT o mysql_affected_rows() per scoprire quante righe sono state coinvolte da un'istruzione DELETE, INSERT, REPLACE o UPDATE.
Solo per le istruzioni SELECT, SHOW, DESCRIBE o EXPLAIN, mysql_query() restituisce un nuovo identificativo di risultato che si può passare a mysql_fetch_array() e ad altre funzioni che si occupano dei risultati delle tabelle. Quando si conclude il trattamento del risultato, si possono liberare le risorse associate ad esso richiamando mysql_free_result(). Comunqe la memoria sarà liberata automaticamente Al termnine dell'esecuzione dello script.
Vedere anche: mysql_num_rows(), mysql_affected_rows(), mysql_unbuffered_query(), mysql_free_result(), mysql_fetch_array(), mysql_fetch_row(), mysql_fetch_assoc(), mysql_result(), mysql_select_db() e mysql_connect().
add a note
User Contributed Notes 26 notes
jack dot whoami at gmail dot com ¶
16 years ago
halion at gmail dot com ¶
16 years ago
mysql_query doesnt support multiple queries, a way round this is to use innodb and transactions
this db class/function will accept an array of arrays of querys, it will auto check every line for affected rows in db, if one is 0 it will rollback and return false, else it will commit and return true, the call to the function is simple and is easy to read etc
----------
class MySQLDB
{
private $connection; // The MySQL database connection
/* Class constructor */
function MySQLDB(){
/* Make connection to database */
$this->connection = mysql_connect(DB_SERVER, DB_USER, DB_PASS) or die(mysql_error());
mysql_select_db(DB_NAME, $this->connection) or die(mysql_error());
}
/* Transactions functions */
function begin(){
$null = mysql_query("START TRANSACTION", $this->connection);
return mysql_query("BEGIN", $this->connection);
}
function commit(){
return mysql_query("COMMIT", $this->connection);
}
function rollback(){
return mysql_query("ROLLBACK", $this->connection);
}
function transaction($q_array){
$retval = 1;
$this->begin();
foreach($q_array as $qa){
$result = mysql_query($qa['query'], $this->connection);
if(mysql_affected_rows() == 0){ $retval = 0; }
}
if($retval == 0){
$this->rollback();
return false;
}else{
$this->commit();
return true;
}
}
};
/* Create database connection object */
$database = new MySQLDB;
// then from anywhere else simply put the transaction queries in an array or arrays like this:
function function(){
global $database;
$q = array (
array("query" => "UPDATE table WHERE something = 'something'"),
array("query" => "UPDATE table WHERE something_else = 'something_else'"),
array("query" => "DELETE FROM table WHERE something_else2 = 'something_else2'"),
);
$database->transaction($q);
}
davidc at edeca dot net ¶
20 years ago
Regarding the idea for returning all possible values of an enum field, the mySQL manual says that "SHOW COLUMNS FROM table LIKE column" should be used to do this.
The function below (presumes db connection) will return an array of the possible values of an enum.
function GetEnumValues($Table,$Column)
{
$dbSQL = "SHOW COLUMNS FROM ".$Table." LIKE '".$Column."'";
$dbQuery = mysql_query($dbSQL);
$dbRow = mysql_fetch_assoc($dbQuery);
$EnumValues = $dbRow["Type"];
$EnumValues = substr($EnumValues, 6, strlen($EnumValues)-8);
$EnumValues = str_replace("','",",",$EnumValues);
return explode(",",$EnumValues);
}
Cavaets:
1) If the LIKE matches more than one column you get the enum from the first, so be careful with the $Column argument
2) You can't have ',' as part of one of the enums (I guess mySQL would escape this, but I haven't tried)
3) If the field isn't an enum you'll get garbage back!
This is just a quick example to show how to do it, some tidying up needs to be done (ie checking if the field is actually an enum) before it is perfect.
fbraz3 at gmail dot com ¶
5 years ago
This project implements a wrapper to mysql functions in PHP7.0+
https://github.com/OOPS-ORG-PHP/mysql-extension-wrapper
tested and working fine =)
nikhil-php at nols dot com ¶
23 years ago
When trying to INSERT or UPDATE and trying to put a large amount of text or data (blob) into a mysql table you might run into problems.
In mysql.err you might see:
Packet too large (73904)
To fix you just have to start up mysql with the option -O max_allowed_packet=maxsize
You would just replace maxsize with the max size you want to insert, the default is 65536
Mr. Tim ¶
15 years ago
It should be noted that mysql_query can generate an E_WARNING (not documented). The warning that I hit was when the db user did not have permission to execute a UDF.
Expected behavior would be like an Invalid SQL statement, where there is no E_WARNING generated by mysql_query.
Warning: mysql_query() [function.mysql-query]: Unable to save result set in filename.php
The mysql_errno is 1370 and the mysql_error is:
execute command denied to user 'username'@'%' for routine 'database_name.MyUDF'
Anonymous ¶
17 years ago
If, like me, you come from perl, you may not like having to use sprintf to 'simulate' placeholders that the DBI package from perl provides. I have created the following wrapper function for mysql_query() that allows you to use '?' characters to substitute values in your DB queries. Note that this is not how DBI in perl handles placeholders, but it's pretty similar.
<?php
// mysql_query() wrapper. takes two arguments. first
// is the query with '?' placeholders in it. second argument
// is an array containing the values to substitute in place
// of the placeholders (in order, of course).
function mysql_prepare ($query, $phs = array()) {
foreach ($phs as $ph) {
$ph = "'" . mysql_real_escape_string($ph) . "'";
$query = substr_replace(
$query, $ph, strpos($query, '?'), 1
);
}
return mysql_query($query);
}
// sample usage
list($user, $passwd) = array('myuser', 'mypass');
$sth = mysql_prepare(
'select userid from users where userid=? and passwd=?',
array($user, sha1($passwd))
);
$row = mysql_fetch_row($sth);
// successfull username & password authentication
if ($row !== false) {
echo "logging in as '{$row[0]}'!\n";
}
// oops, wrong userid or passwd
else {
echo "Invalid username and password combination.\n";
}
?>
ialsoagree ¶
14 years ago
When you run a select statement and receive a response, the data types of your response will be a string regardless of the data type of the column.
<?php
// Query to select an int column
$query = 'SELECT user_id FROM users WHERE user_id = 1';
$result = mysql_query($query);
$array = mysql_fetch_assoc($result);
// Echoes: string
echo gettype($array['user_id']);
?>
ddlshack [at] gmail.dot.com ¶
12 years ago
Use this to neatly insert data into a mysql table:
<?php
function mysql_insert($table, $inserts) {
$values = array_map('mysql_real_escape_string', array_values($inserts));
$keys = array_keys($inserts);
return mysql_query('INSERT INTO `'.$table.'` (`'.implode('`,`', $keys).'`) VALUES (\''.implode('\',\'', $values).'\')');
}
?>
For example:
<?php
mysql_insert('cars', array(
'make' => 'Aston Martin',
'model' => 'DB9',
'year' => '2009',
));
?>
php at arcannon dot com ¶
18 years ago
I believe there is a typo in celtic at raven-blue dot com version with:
if (($sql != "") && (substr($tsl, 0, 2) != "--") && (substr($tsl, 0, 1) != "#")) {
I think you really ment:
if (($tsl != "") && (substr($tsl, 0, 2) != "--") && (substr($tsl, 0, 1) != "#")) {
I changed the $sql to $tsl
masteracc0 at aol dot com ¶
16 years ago
Keep in mind when dealing with PHP & MySQL that sending a null-terminated string to a MySQL query can be misleading if you use echo($sql) in PHP because the null terminator may not be visible.
For example (this assumes connection is already made),
$string1 = "mystring\0";
$string2 = "mystring";
$query1 = "SELECT * FROM table WHERE mystring='".$string1."'"
$query2 = "SELECT * FROM table WHERE mystring='".$string2."'"
$result1 = mysql_query($query1);
$result2 = mysql_query($query2);
//$result1 IS NOT EQUAL TO $result2 but will not provide an error
//but printing these queries to the screen will provide the same result
echo($result1);
echo($result2);
Not knowing this could lead to some mind-numbing troubleshooting when dealing with any strings with a null terminator. So now you know! :)
rob desbois ¶
17 years ago
Note that the 'source' command used in the mysql client program is *not* a feature of the server but of the client.
This means that you cannot do
mysql_query('source myfile.sql');
You will get a syntax error. Use LOAD DATA INFILE as an alternative.
veyita_angi at hotmail dot com ¶
17 years ago
this could be a nice way to print values from 2 tables with a foreign key. i have not yet tested correctly but it should work fine.
$buscar = mysql_query("SELECT k.*, e.Clasificacion FROM cat_plan_k k, cat_equipo e WHERE Tipo='$tipo' AND k.ID_Eq=a.ID_Eq");
while ($row=mysql_fetch_array($buscar))
{
$nombre = "e.Clasificacion";
$row[$nombre] = $Clasific; echo $row[$nombre].'convertido en '.$Clasific;
}
mysql_free_result($buscar);
cc+php at c2se dot com ¶
17 years ago
Here's a parameterised query function for MySQL similar to pg_query_params, I've been using something similar for a while now and while there is a slight drop in speed, it's far better than making a mistake escaping the parameters of your query and allowing an SQL injection attack on your server.
<?php # Parameterised query implementation for MySQL (similar PostgreSQL's PHP function pg_query_params)
# Example: mysql_query_params( "SELECT * FROM my_table WHERE col1=$1 AND col2=$2", array( 42, "It's ok" ) );
if( !function_exists( 'mysql_query_params' ) ) {
function mysql_query_params__callback( $at ) {
global $mysql_query_params__parameters;
return $mysql_query_params__parameters[ $at[1]-1 ];
}
function mysql_query_params( $query, $parameters=array(), $database=false ) {
// Escape parameters as required & build parameters for callback function
global $mysql_query_params__parameters;
foreach( $parameters as $k=>$v )
$parameters[$k] = ( is_int( $v ) ? $v : ( NULL===$v ? 'NULL' : "'".mysql_real_escape_string( $v )."'" ) );
$mysql_query_params__parameters = $parameters;
// Call using mysql_query
if( false===$database )
return mysql_query( preg_replace_callback( '/\$([0-9]+)/', 'mysql_query_params__callback', $query ) );
else return mysql_query( preg_replace_callback( '/\$([0-9]+)/', 'mysql_query_params__callback', $query ), $database );
}
}
?>
fernandoleal at loytek dot com ¶
15 years ago
Dunno if is it a bug but when you are working with replications servers and work with multiple databases queries if you don't select the database it will only insert,update,delete into the master and bypass the slave, I think it its because it doesn't insert the sql on the binary log so the work around its to just call mysql_select_db
MYSQL : 5.0.51a-log
PHP: 5.2.6
Example:
<?php
#Inserts only to master
$link=mysql_connect('host','user','pass');
$sql ="INSERT INTO mysql.host (host) VALUES ('localhost');"
var_dump(mysql_query($sql,$link));
#The Working Way Master - Slave
$link2=mysql_connect('host','user','pass');
$select_db = mysql_select_db('mysql', $link2);
var_dump(mysql_query($sql,$link2));
?>
Anonymous ¶
20 years ago
Until this function prohibits them, watch out for SQL comments (--) in your input.
rogier ¶
15 years ago
For all you programmers out there getting the 'Command out of synch' errors when executing a stored procedure call:
There are known bugs related to this issue, and the best workaround for avoiding this error seems to be switching to mysqli.
Still, I needed mysql to also handle these calls correctly.
The error is normally related to wrong function call sequences, though the bug report at http://bugs.php.net/bug.php?id=39727 shows otherwise.
For me, after commenting out hundreds of lines and several introspection calls to parse the procedure information (using information_schema and 'SHOW' extensions), I still got the same error.
The first result is returned, because I initiated my connection using the MYSQL_MULTI_RESULTS value of 131072 (forget this and you will never get any output, but an error message stating mysql cannot return results in this context)
After testing with this code (sproc2 simply calls 'SELECT * FROM sometable'), I found the error must be in the mysql library/extension. Somehow, mysql does not handle multiple resultsets correctly, or is at least missing some functionality related to handling multiple results.
<?php
//...
$rs = mysql_query('CALL sproc2(500)');
while (($row=mysql_fetch_assoc($rs))!==false) {
print_r($row);
}
mysql_free_result($rs);
$rs = mysql_query('CALL sproc2(500)');
print mysql_error(); //the notorious 'command out of synch' message :(
while (($row=mysql_fetch_assoc($rs))!==false) {
print_r($row);
}
mysql_free_result($rs);
?>
After spending hours debugging my code (the full library is already over the MB), the only solution seemed to be to CLOSE the connection after the first call, and reopening it before the second.
So if you ever make a uniform database accessing interface and implement stored procedures/prepared statements (or classes for it), this could be a solution if you really wish to enable stored procedures.
Still, be aware that this is really a serious flaw in your design (and IMHO, the mysql extension)
Also see the documentation for mysqli on mysqli_query, which seems to be working fine.
ix at nivelzero dot ro ¶
18 years ago
here's a script for parsing a *.sql file (tested only on dumps created with phpMyAdmin) which is short and simple (why do people say "here's a short and simple script" and it has a 100 lines?). the script skips comments and allows ; to be present within the querys
<?php
function parse_mysql_dump($url){
$file_content = file($url);
$query = "";
foreach($file_content as $sql_line){
if(trim($sql_line) != "" && strpos($sql_line, "--") === false){
$query .= $sql_line;
if(preg_match("/;[\040]*\$/", $sql_line)){
$result = mysql_query($query)or die(mysql_error());
$query = "";
}
}
}
}
?>
Anonymous ¶
14 years ago
When processing a RENAME TABLE query, PHP apparently always returns false, no matter if the query was successfully processed or not.
mwwaygoo at hotmail dot com ¶
11 years ago
I much prefer to use the same syntax for single INSERT, REPLACE and UPDATE queries as it is easier to read and keeps my code shorter (no seperate building of insert and update values)
INSERT INTO table SET x='1', y=3
UPDATE table SET x='2' WHERE y=3
So if your using a function to build your query, you will only ever need to code the "field=value, field2=value2" part for any query.
jon at websandbox dot net ¶
18 years ago
I think it's important to note (for newbies, like me especially) that an empty result is not the same as an error:
<?php
/* 'bar' is an empty table in the db */
$rs = mysql_query("SELECT `foo` FROM `bar`")
if($rs) {
echo mysql_num_rows($rs); //outputs: 0
}
/* malformed query /*
$rs = mysql_query("SELECT `foo` FRO `bar`");
if($rs) {
echo "This will never be echoed";
}
?>
allen a brooker gb net ¶
20 years ago
One way to reduce the dangers of queries like the dlete command above that dletes the whole DB is to use limits wherever possible.
EG. If you have a routine that is only deisnged to delete 1 record, add 'LIMIT 1' to the end of the command. This way you'll only lose one record if someone does something stupid.
You should also check all input, especially if it is sent using GET. ie. make sure that $_GET['id'] is not NULL or == "", is a number that is positive, not 0 (generally, I know this doesn't apply to some table types, but it applies to the default) and is within the valid range for that field.
Just don't trust ANY data that is sent to your script.
HTH
Allen
Predrag Supurovic ¶
20 years ago
If you need to execute sevaral SQL commands in a row (usually called batcg SQL) using PHP you canot use mysql_query() since it can execute single command only.
Here is simple but effective function that can run batch SQL commands. Take cere, if string contains semicolon (;) anywhere except as command delimiter (within string expression for example) function will not work.
function mysql_exec_batch ($p_query, $p_transaction_safe = true) {
if ($p_transaction_safe) {
$p_query = 'START TRANSACTION;' . $p_query . '; COMMIT;';
};
$query_split = preg_split ("/[;]+/", $p_query);
foreach ($query_split as $command_line) {
$command_line = trim($command_line);
if ($command_line != '') {
$query_result = mysql_query($command_line);
if ($query_result == 0) {
break;
};
};
};
return $query_result;
}
Richie (at) RichieBartlett.com ¶
14 years ago
For those of you whom spent hours bashing your brains against the keyboard wondering why your non-English characters are output as question marks... Try the following:
<?php
$db = mysql_connect('YOUR_DB_ADDRESS','YOUR_DB_USER','YOUR_DB_PASS') or die("Database error");
mysql_select_db('YOUR_DB', $db);
//SOLUTION:: add this comment before your 1st query -- force multiLanuage support
$result = mysql_query("set names 'utf8'");
$query = "select * from YOUR_DB_TABLE";
$result = mysql_query($query);
//-THE_REST_IS_UP_TO_YOU-
?>
Simply run the query "set names 'utf8' " against the MySQL DB and your output should appear correct.
chris at hotmail dot com ¶
20 years ago
Windows programmers, keep in mind that although table names in Windows queries are not case sensitive, many *NIX versions of Mysql require the correct table name case (perhaps others as well). So you're better off using the right case from the beginning, in case you ever decide to go with a *NIX server.
wjyong at sh163 dot net ¶
18 years ago
The following query is not valid as expected:
<?php
$username = 'dicteworld';
$username{4} = '';
$sql = "SELECT * FROM `user` WHERE `User` = '$username'";
print($sql); // Result: SELECT * FROM `user` WHERE `User` = 'dictworld'
$res = mysql_query($query);
$row = mysql_fetch_array($res);
print_r($row);// Result: still return Array(), supposed that the user 'dictworld' exists.
?>
Pay more attention that null string '' is equivalent to '\0',therefore SQL statement above is equivalent to SELECT * FROM `user` WHERE `User` = 'dict\0world',though printing string is right.
