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 — MySQL 질의를 전송
설명
resource mysql_query
( string
$query
[, resource $link_identifier
] )
mysql_query()는 link_identifier로
지정한 데이터베이스 서버에 하나의 질의를 전송합니다. (다중 질의는 지원하지
않습니다)
인수
-
query -
SQL 질의
질의 문자열은 세미콜론으로 끝나지 않아야 합니다.
-
link_identifier -
MySQL 연결. 지정하지 않으면 mysql_connect()로 연 마지막 연결을 사용합니다. 연결이 없으면, 인수 없이 mysql_connect()를 호출하여 연결을 만듭니다. 연결이 성립되지 않으면
E_WARNING등급의 오류를 생성합니다.
반환값
mysql_query()는 SELECT, SHOW, DESCRIBE, EXPLAIN,
결과셋을 반환하는 기타 구문에서 성공시 resource를, 오류시
FALSE를 반환합니다.
mysql_query()는 다른 형식의 SQL 구문, INSERT, UPDATE,
DELETE, DROP 등에서 성공하면 TRUE를, 실패하면 FALSE를 반환합니다.
반환되는 결과 리소스는 mysql_fetch_array()와 같은 결과 테이블을 다루는 함수들에 전달하여 데이터에 접근할 수 있다.
SELECT 구문으로 부터 얼마나 많은 행이 있는지 알기 위해서는 mysql_num_rows()를, DELETE, INSERT, REPLACE, UPDATE 구문으로 변경된 행의 개수를 알기 위해서는 mysql_affected_rows()를 사용한다.
질의에 의해 참조되는 테이블에 접근을 허용되지 않은 사용자에 의해
mysql_query()가 실패하면 FALSE를 반환한다.
예제
Example #1 잘못된 질의
다음 질의는 문법적으로 오류가 있어서
mysql_query()는 실패하고,
FALSE를 반환한다.
<?php
$result = mysql_query('SELECT * WHERE 1=1');
if (!$result) {
die('Invalid query: ' . mysql_error());
}
?>
Example #2 유효한 질의
다음 질의는 유효한 질의로서 mysql_query()는 resource를 반환한다.
<?php
// 사용자에 의해서 주어집니다. 예를 들면,
$firstname = 'fred';
$lastname = 'fox';
// 질의 만들기
// SQL 질의를 수행하는 가장 좋은 방법입니다
// 더 많은 예제는, mysql_real_escape_string()을 참고하십시오
$query = sprintf("SELECT firstname, lastname, address, age FROM friends WHERE firstname='%s' AND lastname='%s'",
mysql_real_escape_string($firstname),
mysql_real_escape_string($lastname));
// 질의 수행
$result = mysql_query($query);
// 결과 확인
// 실제 질의가 MySQL로 전해지고, 오류가 발생했을 경우입니다. 디버깅에 유용합니다.
if (!$result) {
$message = 'Invalid query: ' . mysql_error() . "\n";
$message .= 'Whole query: ' . $query;
die($message);
}
// 결과 사용하기
// $result를 출력하려고 하면, resource 내부 정보에 접근할 수 없습니다.
// mysql 결과 함수 중 하나를 사용해야 합니다.
// mysql_result(), mysql_fetch_array(), mysql_fetch_row() 등을 참고하십시오.
while ($row = mysql_fetch_assoc($result)) {
echo $row['firstname'];
echo $row['lastname'];
echo $row['address'];
echo $row['age'];
}
// 결과셋으로 할당된 리소스를 해제합니다
// 스크립트 종료 시에 자동으로 이루어집니다
mysql_free_result($result);
?>
참고
- mysql_connect() - MySQL 서버에 접속
- mysql_error() - 최근 실행된 MySQL 작업으로 발생한 에러 메시지를 반환
- mysql_real_escape_string() - mysql_query에서 특수 문자열을 이스케이프하기위해 사용
- mysql_result() - 결과 데이터를 반환
- mysql_fetch_assoc() - 연관 배열로 결과 행을 반환
- mysql_unbuffered_query() - 결과 행을 버퍼링하지도 인출하지도 않으면서 MySQL로 SQL 질의를 전송
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 ¶
21 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 ¶
24 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 ¶
18 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 ¶
15 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($array['user_id']);
?>
ddlshack [at] gmail.dot.com ¶
13 years ago
Use this to neatly insert data into a mysql table:
<?php
function mysql_insert($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 ¶
21 years ago
Until this function prohibits them, watch out for SQL comments (--) in your input.
rogier ¶
16 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 ¶
12 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 ¶
19 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 ¶
21 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.
