Programmatically get relation between tables mysql - php

Question

Assume that I have 3 tables namely sales_order , sales_order_items , invoice and set ON UPDATE = NO ACTION ON DELETE = NO ACTION.
Now I need to have the ability do delete the sales order. But if there is a relation exists in any other table it means that that sales order is used somewhere else and i need to prevent deletion.
Ex: I have sales_order_id = 34 , I want to check its exists in any other tables.
Previously to achieve the same thing I used transactions, something like below
$db = new database();
//start transaction
$db->start_trans();
//try to delete the sales order with ID = 34
$db->exec( 'DELETE FROM SALES_ORDER WHERE ID = 34' );
//check transaction success or failure
if( $db->trans_status() == true ){
//THERE IS NO RELATION EXISTS
//ROLLBACK
$db->rollback_trans();
#Soft Delete the record
$db->exec( 'UPDATE sales_order SET is_deleted = 1 WHERE id = 34' );
}else{
//RELATION EXISTS FOR ID = 34 IN SOME OTHER TABLES
}
the above code works, but the problem is with sales_order_items. Because it is a child table of sales_order and if it have contents then the transaction will fail and will try to execute the else part.
But in fact sales_order_items is a property of sales_order and I need to DELETE that particular sales_order (don't care about items).
I am expecting something like this
$relations = $db->get_relation( 'sales_order.id', '34' );
Expected Output
array( 'sales_order_items','invoice','another_table' .... );
Note: The above is an example only, I have number of tables and it's not possible to go through each table and check ID exists.

Answer 1

select * from information_schema.table_constraints
where constraint_schema = DATABASE();
select * from information_schema.key_column_usage
where constraint_schema = DATABASE();
SQLFIDDLE

Answer 2

Thanks Revoua for providing a good answer. Here is little modified version to suite my needs. Please correct me if it have some better way.
function check_relation( $table_name , $table_column ,$table_value ){
//Get relation tables
$qry = "SELECT table_name,
column_name,
referenced_table_name,
referenced_column_name
FROM information_schema.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_SCHEMA = ?
AND REFERENCED_TABLE_NAME is not null
AND referenced_table_name = ?
AND referenced_column_name = ?";
$db = $this->crm->db;
//database name
$database = $db->dbprefix.$db->database;
//predefined array to store table names
$related_tables = array();
//execute the query
$qry = $db->query( $qry , array( $database , $table_name ,$table_column ) );
unset($database);
//Make sure that query is success
if( $qry != FALSE && $qry->row_count() > 0 ){
//Get as array
$result = $qry->to_array();
unset($qry);
foreach( $result as $result_item ){
//Get count based on table_value
$qry = "SELECT COUNT(*)as total FROM ".$result_item['table_name']." WHERE ".$result_item['column_name']." = ? and is_del = 0";
$qry = $db->query($qry,array($table_value));
if( $qry!= FALSE && $qry->row_count() > 0 ) {
$qry = $qry->to_array(1);
//There are some entries ..
if( intval($qry['total']) > 0 ){
$related_tables[] = $result_item['table_name'];
}
}
}
return $related_tables;
}else{
return $related_tables;
}
}
Usage:
$relation = $db->check_relation("SALES_ORDER","ID",34);
var_dump( $relation ) ==>
array( 'SALES_ORDER_ITEM','INVOICE' ... );
Now in business logic
if( empty( $relation ) ){
// No relation exists
}elseif( in_array( 'invoice', $relation ) ){
$message->set_message("Cannot delete Sales Order, Invoice exists.");
}else ...