How can I delete data from database with foreign key constraint in mysql using PHP pdo

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I have three Tables in database.

table 1

projects

PK ProjectID

table 2

students

PK RegNo FK ProjectID table 3

progress FK RegNo

Now the thing i want to perform a delete operation when i delete record from project it should be deleted from students, as students primary key is also present as foreign key progress table, so it should also delete RegNo from progress table. How i can achieve this as the best possible way. Thanks in advance.

What I have tried:

PHP

$query = "

        DELETE students, progress from students inner join progress on progress.RegNo=students.RegNo where students.ProjectID='$id';
        DELETE FROM projects where projects.ProjectID='$id'; 
";

//$conn->exec($query);
$stmt = $conn->prepare($query); $stmt->execute();

it gives foreign key constraint violation

Posted 7-Jun-18 2:08am

Ameer111

Updated 11-Sep-20 23:02pm

Patrice T

v2

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Richard Deeming · Answer 1 · 2018-06-07T04:28:00

Option 1:
Set the foreign key to cascade on delete:
MySQL ON DELETE CASCADE: Deleting Data From Multiple Tables[^]

Option 2:
Delete the data from all related tables manually:

SQL

DELETE FROM progress FROM progress INNER JOIN students ON progress.RegNo = students.RegNo WHERE students.ProjectID = :id;
DELETE FROM students WHERE students.ProjectID = :id;
DELETE FROM projects WHERE projects.ProjectID = :id;

NB: Use parameters to pass values to the query, rather than inserting the values directly into the string. If you don't, you can make your code vulnerable to SQL Injection.

Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^]
How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^]
Query Parameterization Cheat Sheet | OWASP[^]
PHP: SQL Injection - Manual[^]
PHP: Prepared statements and stored procedures - Manual[^]

Patrice T · Answer 2 · 2018-06-07T12:03:00

PHP

$query = "
        DELETE students, progress from students inner join progress on progress.RegNo=students.RegNo where students.ProjectID='$id';
        DELETE FROM projects where projects.ProjectID='$id'; 
";

Not a solution to your question, but another problem you have.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[^]
SQL Injection[^]
SQL Injection Attacks by Example[^]
PHP: SQL Injection - Manual[^]
SQL Injection Prevention Cheat Sheet - OWASP[^]
How can I explain SQL injection without technical jargon? - Information Security Stack Exchange[^]

How can I delete data from database with foreign key constraint in mysql using PHP pdo

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