MySQL查询在php中不起作用，直接运行时可以正常工作

Question

I have a very strange problem with MySQL and PHP.

I have into a function the below query:

Global $Linker;

$query = "INSERT INTO ".$user_type." (id) VALUES (?)";

if($stmt = mysqli_prepare($Linker->DataBase,$query)) {

            mysqli_stmt_bind_param($stmt,"i",$max_id);
            mysqli_stmt_execute($stmt);     
            mysqli_stmt_close($stmt); 

} printf("Error: %s.
", mysqli_stmt_error($stmt));

where

$Linker is the variable that holds the database connection

and

$user_type is the table I want to insert in the database

I get the following error printed

Error: Cannot add or update a child row: a foreign key constraint fails (std10179db/Students, CONSTRAINT fk_Students_Users1 FOREIGN KEY (id) REFERENCES mydb.Users (Table_ID) ON DELETE NO ACTION ON UPDATE NO ACTION).

The problem is that when I run the same query directly in MySQL through command line in the server it works as expected with no errors.

I found a work around using:

$query= "SET FOREIGN_KEY_CHECKS=0";
$stmt = mysqli_prepare($Linker->DataBase,$query);
mysqli_stmt_execute($stmt);
mysqli_stmt_close($stmt); 

before my query in the PHP function and another workaround would be to change my database schema but I want to know why that is happening?

I have even tried to execute the query without parameters:

$query = "INSERT INTO Students (id) VALUES (3)";

to be exactly the same with the one I put directly into the server with no success.

Any ideas?

edit:

Table USERS

CREATE  TABLE `std10179db`.`Users` (
`ID` INT NOT NULL ,
`Username` VARCHAR(45) NOT NULL ,
`Password` VARCHAR(45) NOT NULL ,
`email` VARCHAR(45) NOT NULL ,
`User_Class` VARCHAR(45) NOT NULL ,
`Table_ID` INT NOT NULL ,
PRIMARY KEY (`ID`) ,
UNIQUE INDEX `Username_UNIQUE` (`Username` ASC) ,
UNIQUE INDEX `Password_UNIQUE` (`Password` ASC) ,
UNIQUE INDEX `email_UNIQUE` (`email` ASC) )
ENGINE = InnoDB;

and Table Students

  CREATE  TABLE `std10179db`.`Students` (
  `id` INT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `Univ_ID` VARCHAR(45) NULL ,
  `Name` VARCHAR(45) NULL ,
  `Surname` VARCHAR(45) NULL ,
  `Telephone` VARCHAR(45) NULL ,
  `Semester` INT NULL ,
  `Department_id` INT UNSIGNED NULL ,
  PRIMARY KEY (`id`, `Department_id`) ,
  UNIQUE INDEX `idStudents_UNIQUE` (`id` ASC) ,
  INDEX `fk_Students_Department1` (`Department_id` ASC) ,
  CONSTRAINT `fk_Students_Department1`
    FOREIGN KEY (`Department_id` )
    REFERENCES `mydb`.`Department` (`id` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_Students_Users1`
    FOREIGN KEY (`id` )
    REFERENCES `mydb`.`Users` (`Table_ID` )
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)
ENGINE = InnoDB;