Asked  7 Months ago    Answers:  5   Viewed   27 times

I work with xampp. I performed MySQL connection:

$connection = mysql_connect($host , $user , $passw);
mysql_select_db($db, $connection);

I received output with echo command (by check the boolean returned values) that connection is established and the database $db is found.

But the simplest query like:

$query = mysql_query("SELECT * FROM 'users'");

returns false. How can I debug why?Thanks.

 Answers

85

An obligatory update: as mysql ext is no more, here are answers for two remaining MySQL APIs which I written on my site based on the experience from answering 1000s questions on Stack Overflow:

  • How to report errors in mysqli
  • How to connect to MySQL using PDO (with the aim of the proper error reporting).

In short, for mysqi the following line have to be added before mysqli_connect() call:

mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

while for PDO the proper error mode have to be set, for example

$pdo->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

As of the old mysql ext,

To get an error from mysql_query() you have to use mysql_error() function.
So always run all your queries this way, at least until you develop a more advanced query handler:

$query = "SELECT * FROM 'users'";
$result = mysql_query($query) or trigger_error(mysql_error()." ".$query);

the problem with your current query is 'users' part. Single quotes have to be used to delimit strings while for the identifiers you have to use backticks:

SELECT * FROM `users`

In order to see these errors during development, add these lines at the top of your code to be sure you can see every error occurred

ini_set('display_errors',1);
error_reporting(E_ALL);

on the production server, however, the value on the first line should be changed from 1 to 0

Wednesday, March 31, 2021
 
Ula
answered 7 Months ago
Ula
71

you can't print the result from mysqli_query, it is mysqli_resource and for dumping the error you need to change mysql_error() to mysqli_error()

$username = "bob";
$db = mysqli_connect("localhost", "username", "password", "user_data");
$sql1 = "select id from user_information where username='$username'";
$result = mysqli_query($db, $sql1) or die(mysqli_error());
while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) { 
    echo $row['id'].'<br>'; 
} 
Saturday, May 29, 2021
 
pamelus
answered 5 Months ago
53

Perhaps you could create an indexing table which provides a sequential key relating to the key in your target table. Then you can join this indexing table to your target table and use a where clause to more efficiently get the rows you want.

#create table to store sequences
CREATE TABLE seq (
   seq_no int not null auto_increment,
   id int not null,
   primary key(seq_no),
   unique(id)
);

#create the sequence
TRUNCATE seq;
INSERT INTO seq (id) SELECT id FROM mytable ORDER BY id;

#now get 1000 rows from offset 1000000
SELECT mytable.* 
FROM mytable 
INNER JOIN seq USING(id)
WHERE seq.seq_no BETWEEN 1000000 AND 1000999;
Thursday, June 3, 2021
 
ritch
answered 5 Months ago
92
mysql>show processlist;

mysql> kill "number from first col";
Sunday, June 27, 2021
 
Kevin_Kinsey
answered 4 Months ago
39

yo need create the user "pma" in mysql or change this lines(user and password for mysql):

/* User for advanced features */
$cfg['Servers'][$i]['controluser'] = 'pma'; 
$cfg['Servers'][$i]['controlpass'] = '';

Linux: /etc/phpmyadmin/config.inc.php

Tuesday, July 13, 2021
 
ShadowZzz
answered 3 Months ago
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