¿Cómo saber si registro tiene referencias a través de FK?

[huesos52]

Con information_schema puedes obtener algunos datos. Mira algunos ejemplos.

Código MYSQL:

mysql> desc cobros;
+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| id       | int(11)      | NO   | PRI | NULL    | auto_increment |
| fecha    | date         | NO   |     |         |                |
| unidad   | varchar(3)   | NO   | MUL |         |                |
| cuotadm  | float        | NO   |     |         |                |
| parq     | float        | NO   |     |         |                |
| otros    | float        | NO   |     |         |                |
| concepto | varchar(120) | NO   |     |         |                |
+----------+--------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)
 
mysql> desc unidad;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| uniresi   | varchar(3)  | NO   | PRI |         |       |
| estado    | varchar(10) | NO   |     |         |       |
| arriendo  | varchar(2)  | NO   |     |         |       |
| numhab    | int(2)      | NO   |     |         |       |
| parq      | varchar(2)  | NO   |     |         |       |
| numparq   | int(10)     | NO   |     |         |       |
| mascota   | varchar(2)  | NO   |     |         |       |
| matricula | varchar(20) | YES  |     | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
8 rows in set (0.00 sec)
 
mysql> select constraint_name,constraint_type,table_name,table_schema from information_schema.table_constraints where table_name = 'cobros' and table_schema='sgh';
+-----------------+-----------------+------------+--------------+
| constraint_name | constraint_type | table_name | table_schema |
+-----------------+-----------------+------------+--------------+
| PRIMARY         | PRIMARY KEY     | cobros     | sgh          |
| cobros_ibfk_1   | FOREIGN KEY     | cobros     | sgh          |
+-----------------+-----------------+------------+--------------+
2 rows in set (0.00 sec)
 
mysql> select constraint_name,constraint_type,table_name,table_schema from information_schema.table_constraints where table_name = 'unidad' and table_schema='sgh';
+-----------------+-----------------+------------+--------------+
| constraint_name | constraint_type | table_name | table_schema |
+-----------------+-----------------+------------+--------------+
| PRIMARY         | PRIMARY KEY     | unidad     | sgh          |
+-----------------+-----------------+------------+--------------+
1 row in set (0.00 sec)
 
mysql> select count(*) conteo from information_schema.table_constraints where table_name = 'cobros' and table_schema='sgh' and constraint_type='FOREIGN KEY';
+--------+
| conteo |
+--------+
|      1 |
+--------+
1 row in set (0.00 sec)
 
mysql>