查询具有一对多关系的两个表

Question

I feel a little embarrassed as there is probably an easy solution, but I don't know enough MySQL to do it. How do I use one query to get data from each of these tables, and then return an array as illustrated below? Every attempt I make ends up returning either one tag, or returning multiple arrays of the same task, each with a different tag.

What should my query structure look like?

Thanks!

http://i.stack.imgur.com/ViqEs.png

Answer 1

The image's array actually shows how the data would look like after two queries, not one. To be able to do it in a single query, and this is because the data is not too complex, you could use a GROUP_CONCAT() to get all of the tags for a task and then use post-query logic to split the data into separate arrays.

The SQL query to get all of the requested data would be:

SELECT
    tasks.*, GROUP_CONCAT(tag_name) AS tags
FROM
    tasks LEFT JOIN tags ON tags.task_id=tags.id
WHERE
    id=2

This query will return a single record; in that record, the column tags will hold a comma-separated list of all of the tags that belong to the task. You can split the data in that column into an array to build your desired structure.

An example, with PHP:

$result = mysql_query("SELECT tasks.*, GROUP_CONCAT(tag_name) AS tags FROM tasks LEFT JOIN tags ON tags.task_id=tags.id WHERE id=2");

// create the "$task" array that has a "task" and "tags" index
$task = array('task' => array(), 'tags' => array());
$task['task'] = mysql_fetch_assoc($result);

// split the comma-separated list of tags into an array
$task['tags'] = explode(',', $task['task']['tags']);

// delete the original "tags" entry that's returned by the sql query
unset($task['task']['tags']);

Please note that this example is void of any data validation, connection information, or other logic and should just be used as a rough idea as how you could split the data into your desired structure.