Question

I have a MySQL database with a few tables. They look something like this –

The food table:

+----------+------------+--------------+
| username | date       | food         |
+----------+------------+--------------+
| test123  | 2012-09-16 | rice         |
| test123  | 2012-09-16 | pizza        |
| test123  | 2012-09-16 | french fries |
| test123  | 2012-09-16 | burger       |
+----------+------------+--------------+

The main table:

+----------+------------+----------------+---------------+-------------+-------------+
| username | date       | water_quantity | water_chilled | smoked_what | smoke_count |
+----------+------------+----------------+---------------+-------------+-------------+
| test123  | 2012-09-16 |              1 | no            | cigarettes  |          20 |
+----------+------------+----------------+---------------+-------------+-------------+

When I use the query SELECT * FROM main,food WHERE main.date=food.date;, I get four rows as a result. How would it be possible that I get the results in a single row? Ultimately, when I encode the results into JSON, I want it to look something like this –

[
   {
      "username":"test123",
      "date":"2012-09-16",
      "water_quantity":"1",
      "water_chilled":"no",
      "smoked_what":"cigarettes",
      "smoke_count":"20",
       {
          "food":"rice",
          "food":"pizza",
          "food":"french fries",
          "food":"burger",                  
       },
   }
]

or something similar to. I am a newbie to MySQL and databases in general and also to JSON.. Thanks in advance for the help.

Answer 1

select m.*, GROUP_CONCAT(food SEPARATOR ',') AS food FROM main m INNER JOIN food f ON f.username = m.username and f.date = m.date;

Of course you can change what fields you select to control the output but that will solve your duplication issue.

As for the nested list of foods within the result set, you can use GROUP_CONCAT

SEE: http://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_group-concat

I will see if I can recreate for demo

---

DEMO:

mysql> create table main (id INT NOT NULL AUTO_INCREMENT, username varchar(12) NOT NULL, date DATETIME, water_quality INT, water_chilled CHAR(3), smoked_what varchar(32), smoke_count INT, primary key (id));
Query OK, 0 rows affected (0.04 sec)

mysql> create table food (id INT NOT NULL AUTO_INCREMENT, username varchar(12) NOT NULL, date DATETIME, food varchar(32), primary key (id));
Query OK, 0 rows affected (0.04 sec)

mysql> insert into food VALUES (1,'test123','2012-09-16','rice'),(2,'test123','2012-09-16','pizza'),(3,'test123','2012-09-16','french fries'),(4,'test123','2012-09-16','burger');Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> insert into main VALUES (1, 'test123', '2012-09-16', 1, 'no', 'cigarettes', 20);
Query OK, 1 row affected (0.00 sec)

mysql> select m.*, GROUP_CONCAT(food SEPARATOR ',') AS food FROM main m INNER JOIN food f ON f.username = m.username and f.date = m.date;
+----+----------+---------------------+---------------+---------------+-------------+-------------+----------------------------------+
| id | username | date                | water_quality | water_chilled | smoked_what | smoke_count | food |
+----+----------+---------------------+---------------+---------------+-------------+-------------+----------------------------------+
|  1 | test123  | 2012-09-16 00:00:00 |             1 | no            | cigarettes  |          20 | rice,pizza,french fries,burger   |
+----+----------+---------------------+---------------+---------------+-------------+-------------+----------------------------------+
1 row in set (0.00 sec)

mysql>