SELECT
table1.id,
table2_A.words colorname,
table2_B.words foodname
FROM table1
LEFT JOIN table2 table2_A ON table1.color=table2_A.id
LEFT JOIN table2 table2_B ON table1.food=table2_B.id;
datos de la muestra
mysql> drop database if exists supercoolville;
Query OK, 2 rows affected (0.06 sec)
mysql> create database supercoolville;
Query OK, 1 row affected (0.00 sec)
mysql> use supercoolville;
Database changed
mysql> create table table1
-> (
-> id int not null auto_increment,
-> color int,
-> food int,
-> primary key (id)
->);
Query OK, 0 rows affected (0.06 sec)
mysql> insert into table1 (color,food) values
-> (1,3),(1,4),(1,3),(1,4),
-> (2,3),(2,4),(2,3),(2,4);
Query OK, 8 rows affected (0.06 sec)
Records: 8 Duplicates: 0 Warnings: 0
mysql> create table table2
-> (
-> id int not null auto_increment,
-> words varchar(20),
-> primary key (id)
->);
Query OK, 0 rows affected (0.05 sec)
mysql> insert into table2 (words) values
-> ('yellow'),('blue'),('cookies'),('milk');
Query OK, 4 rows affected (0.07 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from table1;
+----+-------+------+
| id | color | food |
+----+-------+------+
| 1 | 1 | 3 |
| 2 | 1 | 4 |
| 3 | 1 | 3 |
| 4 | 1 | 4 |
| 5 | 2 | 3 |
| 6 | 2 | 4 |
| 7 | 2 | 3 |
| 8 | 2 | 4 |
+----+-------+------+
8 rows in set (0.01 sec)
mysql> select * from table2;
+----+---------+
| id | words |
+----+---------+
| 1 | yellow |
| 2 | blue |
| 3 | cookies |
| 4 | milk |
+----+---------+
4 rows in set (0.00 sec)
resultados de mis consultas
mysql> SELECT
-> table1.id,
-> table2_A.words colorname,
-> table2_B.words foodname
-> FROM table1
-> LEFT JOIN table2 table2_A ON table1.color=table2_A.id
-> LEFT JOIN table2 table2_B ON table1.food=table2_B.id
-> ;
+----+-----------+----------+
| id | colorname | foodname |
+----+-----------+----------+
| 1 | yellow | cookies |
| 2 | yellow | milk |
| 3 | yellow | cookies |
| 4 | yellow | milk |
| 5 | blue | cookies |
| 6 | blue | milk |
| 7 | blue | cookies |
| 8 | blue | milk |
+----+-----------+----------+
8 rows in set (0.00 sec)
mysql>
ACTUALIZACIÓN 2012-05-14 19:10 EDT
En el caso de que sean los valores para alimentos o colores que no existen, aquí está la consulta ajustada:
SELECT
table1.id,
IFNULL(table2_A.words,'Unknown Color') colorname,
IFNULL(table2_B.words,'Unknown Food') foodname
FROM table1
LEFT JOIN table2 table2_A ON table1.color=table2_A.id
LEFT JOIN table2 table2_B ON table1.food=table2_B.id;
voy a añadir filas a tabla1 y ejecutar esta nueva consulta
mysql> drop database if exists supercoolville;
Query OK, 2 rows affected (0.13 sec)
mysql> create database supercoolville;
Query OK, 1 row affected (0.00 sec)
mysql> use supercoolville;
Database changed
mysql> create table table1
-> (
-> id int not null auto_increment,
-> color int,
-> food int,
-> primary key (id)
->);
Query OK, 0 rows affected (0.08 sec)
mysql> insert into table1 (color,food) values
-> (1,3),(1,4),(1,3),(1,4),
-> (2,3),(2,4),(2,3),(2,4),
-> (5,3),(5,4),(2,6),(2,8);
Query OK, 12 rows affected (0.07 sec)
Records: 12 Duplicates: 0 Warnings: 0
mysql> create table table2
-> (
-> id int not null auto_increment,
-> words varchar(20),
-> primary key (id)
->);
Query OK, 0 rows affected (0.08 sec)
mysql> insert into table2 (words) values
-> ('yellow'),('blue'),('cookies'),('milk');
Query OK, 4 rows affected (0.06 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from table1;
+----+-------+------+
| id | color | food |
+----+-------+------+
| 1 | 1 | 3 |
| 2 | 1 | 4 |
| 3 | 1 | 3 |
| 4 | 1 | 4 |
| 5 | 2 | 3 |
| 6 | 2 | 4 |
| 7 | 2 | 3 |
| 8 | 2 | 4 |
| 9 | 5 | 3 |
| 10 | 5 | 4 |
| 11 | 2 | 6 |
| 12 | 2 | 8 |
+----+-------+------+
12 rows in set (0.00 sec)
mysql> select * from table2;
+----+---------+
| id | words |
+----+---------+
| 1 | yellow |
| 2 | blue |
| 3 | cookies |
| 4 | milk |
+----+---------+
4 rows in set (0.00 sec)
mysql> SELECT
-> table1.id,
-> IFNULL(table2_A.words,'Unknown Color') colorname,
-> IFNULL(table2_B.words,'Unknown Food') foodname
-> FROM table1
-> LEFT JOIN table2 table2_A ON table1.color=table2_A.id
-> LEFT JOIN table2 table2_B ON table1.food=table2_B.id;
+----+---------------+--------------+
| id | colorname | foodname |
+----+---------------+--------------+
| 1 | yellow | cookies |
| 2 | yellow | milk |
| 3 | yellow | cookies |
| 4 | yellow | milk |
| 5 | blue | cookies |
| 6 | blue | milk |
| 7 | blue | cookies |
| 8 | blue | milk |
| 9 | Unknown Color | cookies |
| 10 | Unknown Color | milk |
| 11 | blue | Unknown Food |
| 12 | blue | Unknown Food |
+----+---------------+--------------+
12 rows in set (0.00 sec)
mysql>
Teniendo en cuenta los datos no válidos, en LEFT JOIN
aún necesitaba.
Según los datos que presenta, parece que esto se puede hacer con uniones internas rectas, ¿las uniones de la izquierda son realmente necesarias? –