删除所有外键数据，删除主数据或反之亦然

Question

I have table structure like this:

PrimaryTable -> p_id Here p_id is primary

SecondoryTable -> s_id p_id Here p_id is a foreign key

ThirdTable -> t_id s_id Here s_id is foreign key

FourthTable -> f_id t_id Here t_id is foreign key

So I am deleting one of my p_id from PrimaryTable and want that its SecondoryTable data should also get delete AND ThirdTable data should be deleted with reference to SecondoryTable and FourthTable data should be deleted with reference to ThirdTable

I know i can write Delete query from bottom to top, but how to do for so many levels like this??

I found this but not sure on howto: https://stackoverflow.com/a/9847308/1182021

Because its four level hierarchy i am confused.

EDIT1:

What if I want to delete Primary on Delete of Child

Kindly suggest.

Answer 1

As per OP's request, this is an answer for the case when the user wants to delete the row from the parent table when a row is deleted from the child table. The case for recursively deleting all the children when a parent is deleted is working using MySQL ON DELETE CASCADE option.

The 4 tables would be table1, table2, table3 & table4.

If the user wants to delete a row in table2 and also the corresponding row in table1 (parent of table2) then in PHP:

// t2_delete_row_id is the id of the table 2 row to be deleted
// get the the parent of table2
$sql_get_parent = "select p_id from table2 where s_id = 't2_delete_row_id '";
// execute this query using MySQLi/PDO to get id of the parent row to be deleted
// assuming that id is t1_parent_row_id
// now delete the row from table 2:
// note that because of the foreign key constraints, 
// corresponding rows from table3 and table4 would also be deleted
$sql_delete_child = "delete from table2 where s_id = 't2_delete_row_id'";
if (mysqli_query($sql_delete_child)){
    // delete the parent row
    $sql_delete_parent = "delete from table1 where p_id = 't1_parent_row_id'";
}

this logic can be extended so that on deleting table3 row, corresponding parent(table2) and "grand-parent" (table1) rows would be deleted as well. A bit of recursion might be needed for that case. And this will of course delete the child rows in table4 because of the foreign key constraint.

Answer 2

If you are not able to use FOREIGN KEYS (ie using MyISAM tables) I would create a TRIGGER for this. Example for first one below ... you will need to make one for each table that's cascading.

DELIMITER //
CREATE TRIGGER `pDeleteTrigger` BEFORE DELETE ON `PrimaryTable`
 FOR EACH ROW BEGIN
    DELETE FROM `SecondoryTable` WHERE NEW.`p_id` = `SecondoryTable`.`p_id`
END
//
DELIMITER ;

Answer 3

I have two approachs in my mind (if your language is Tsql)

1.- Store procedure

The idea is have a procedure "spDelete_PrimaryTable", so that you can delete the registers in the four tables by writinf something in tsql like:

 exec spDelete_PrimaryTable
       @p_id= 25 /* (25 or watever p_id of primary table you want to delete)*/

(yes you can call it from vb.net or watever you want to.)

the code would be something like:

use [your_database]

CREATE PROCEDURE [dbo].[spDelete_PrimaryTable]
    @p_id nvarchar(MAX)
AS 
 begin  
    SET NOCOUNT ON;

delete from FourthTable where t_id in (
    select ThirdTable.t_id 
    from ThirdTable inner join SecondoryTable on ThirdTable.s_id = SecondoryTable.s_id
    where SecondoryTable.p_id = @p_id
)
go

delete from ThirdTable where s_id in (
    select SecondoryTable.s_id 
    where SecondoryTable.p_id = @p_id
)
go

    /*Lol, I forgot to eliminate from the "SecondoryTable" */
    delete from SecondoryTable.s_id 
    where SecondoryTable.p_id = @p_id

go

delete from PrimaryTable where p_id = @p_id
go

 END


GO

2.- Triggers

seems like "Christopher Morrissey" have already posted that while i was editing this answer XP