CODEWITHSUNDEEP
mysqlsqlstringwhere-clausesql-injection
Sadriddin Shamsuddinov
Sadriddin Shamsuddinov

Reputation: 11

How this query works in Mysql?

I have a table user with 2 rows

CREATE TABLE `user` (
    `id_user` INT(9) AUTO_INCREMENT,
    `login` VARCHAR(50),
    `passw` VARCHAR(32),
    PRIMARY KEY (`id_user`)
    )  CHARSET=utf8 COLLATE utf8_general_ci;
    INSERT INTO `user` VALUES 
(NULL, 'Admin', '123'),  
(NULL, 'Nik', '456');

then i make a query:

SELECT * FROM `user` WHERE `login` = '' OR ''='' AND `passw`='' OR ''=''

the result :

  1  Admin 123
  2  Nik   456

So how it works? What does it mean ''='' ?

I would be grateful if you could advise literature where I can learn about something similar.

Upvotes: 0

Views: 47

Answers (1)

GMB
GMB

Reputation: 222682

This looks like a SQL injection attempt. This:

WHERE `login` = '' OR ''='' AND `passw`='' OR ''=''

Evaluates as:

WHERE `login` = '' 
    OR (''='' AND `passw`='')
    OR ''=''

Condition '' = '' is always true (the empty string is equal to the empty string), so the WHERE clause evaluates as true for every row of the table: the query returns the whole table.

Upvotes: 4

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