how to convert table columns into a table in mysql? - mysql

Question

I know it's a bad title, but I don't know how to describe my question in a line.
I want to store following information in my database.
+----+----------+-----------+-----------+
| id | name | cluster_1 | cluster_2 |
+----+----------+-----------+-----------+
| 1 | content_1| true| false |
| 2 | content_2| false| true |
| 3 | content_3| true| true |
+----+----------+-----------+-----------+
cluster_1=true means that the content exists on the cluster_1.
As some clusters may added or deleted, I want to store my cluster information in a new table "clusters", and indicate the relation between contents and clusters with a "content_cluster" table.
table contents
+----+----------+
| id | name |
+----+----------+
| 1 | content_1|
| 2 | content_2|
| 3 | content_3|
+----+----------+
table clusters
+----+----------+
| id | name |
+----+----------+
| 1 | cluster_1|
| 2 | cluster_2|
+----+----------+
table content_cluster
+----------+----------+
|content_id|cluster_id|
+----------+----------+
| 1 | 1 |
| 2 | 2 |
| 3 | 1 |
| 3 | 2 |
+----------+----------+
But, writing in this way, I don't know how to get a content which is on cluster_1 but isn't on cluster_2, or vice versa. I have to do this query frequently. So what is the efficient way to do this?

Answer 1

how to get a content which is on cluster_1 but isn't on cluster_2
in general
SELECT contents.name
FROM contents
JOIN content_cluster ON contents.id = content_cluster.content_id
LEFT JOIN clusters ON clusters.id = content_cluster.cluster_id
GROUP BY contents.name
HAVING SUM(clusters.name = 'cluster_1') -- not zero, may add ">0"
AND !SUM(clusters.name = 'cluster_2') -- zero, may replace NOT ("!") with "=0"

Answer 2

The following should work:
-- For cluster 1
INSERT INTO new_table (content_id, cluster_id)
SELECT old_table.content_id, 1
FROM old_table
WHERE old_table.cluster_1 = TRUE;
-- For cluster 2
INSERT INTO new_table (content_id, cluster_id)
SELECT old_table.content_id, 2
FROM old_table
WHERE old_table.cluster_2 = TRUE;