MySQL łączy tabele, w których nazwa tabeli jest polem innej tabeli

Jeśli chcesz mieć wszystkie wiersze (wyjście zbiorcze), a nie jeden wiersz na raz, poniższe powinno być szybkie, a wynik dla wszystkich wierszy będzie zawierał wszystkie kolumny.

Select objects.*, typestable.*
from (
    select ID as oID, "mobile" as otype, M1, M2, NULL T1, NULL T2, NULL C1, NULL C2 from obj_mobiles 
    union all
    select ID as oID, "tablet" as otype, NULL, NULL, T1, T2, NULL, NULL from obj_tablets 
    union all
    select ID as oID, "computer" as otype, NULL, NULL, NULL, NULL, C1, C2 from obj_computers) as typestable 
        left join objects on typestable.oID = objects.ID and typestable.otype = objects.type;

+------+--------------------+----------+------+----------+------+------+------+------+------+------+
| ID   | name               | type     | ID   | type     | M1   | M2   | T1   | T2   | C1   | C2   |
+------+--------------------+----------+------+----------+------+------+------+------+------+------+
|    1 | Samsung Galaxy s2  | mobile   |    1 | mobile   |    1 | Thin | NULL | NULL | NULL | NULL |
|    2 | Samsung Galaxy Tab | tablet   |    2 | tablet   | NULL | NULL | 0.98 |   10 | NULL | NULL |
|    3 | Dell Inspiron      | computer |    3 | computer | NULL | NULL | NULL | NULL | 4.98 | 1000 |
+------+--------------------+----------+------+----------+------+------+------+------+------+------+

Tabele są tworzone jak poniżej.

mysql> create table objects (ID int, name varchar(50), type varchar (15));
Query OK, 0 rows affected (0.05 sec)
mysql> insert into objects values (1, "Samsung Galaxy s2", "mobile"), (2, "Samsung Galaxy Tab", "tablet"), (3, "Dell Inspiron", "computer");
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0


mysql> create table obj_mobiles (ID int, M1 int, M2 varchar(10));
Query OK, 0 rows affected (0.03 sec)
mysql> insert into obj_mobiles values (1, 0.98, "Thin");
Query OK, 1 row affected (0.00 sec)


mysql> create table obj_tablets (ID int, T1 float, T2 int(10));
Query OK, 0 rows affected (0.03 sec)
mysql> insert into obj_tablets values (2, 0.98, 10);
Query OK, 1 row affected (0.00 sec)


mysql> create table obj_computers (ID int, C1 float, C2 int(10));
Query OK, 0 rows affected (0.03 sec)
insert into obj_computers values (3, 4.98, 1000);

aby potwierdzić, że typy danych kolumn są takie same jak oryginalne kolumny, wynik jest zapisywany w tabeli, a typy danych są sprawdzane poniżej.

create table temp_result as
Select objects.*, typestable.*
from (
    select ID as oID, "mobile" as otype, M1, M2, NULL T1, NULL T2, NULL C1, NULL C2 from obj_mobiles 
    union all
    select ID as oID, "tablet" as otype, NULL, NULL, T1, T2, NULL, NULL from obj_tablets 
    union all
    select ID as oID, "computer" as otype, NULL, NULL, NULL, NULL, C1, C2 from obj_computers) as typestable 
        left join objects on typestable.oID = objects.ID and typestable.otype = objects.type;

mysql> desc temp_result;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| ID    | int(11)     | YES  |     | NULL    |       |
| name  | varchar(50) | YES  |     | NULL    |       |
| type  | varchar(15) | YES  |     | NULL    |       |
| oID   | int(11)     | YES  |     | NULL    |       |
| otype | varchar(8)  | NO   |     |         |       |
| M1    | int(11)     | YES  |     | NULL    |       |
| M2    | varchar(10) | YES  |     | NULL    |       |
| T1    | float       | YES  |     | NULL    |       |
| T2    | int(11)     | YES  |     | NULL    |       |
| C1    | float       | YES  |     | NULL    |       |
| C2    | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
11 rows in set (0.00 sec)