选择单个单元格中的多个值

Question

Let's say I have the following table, called test :

Executing the query SELECT DISTINCT category FROM test ORDER BY category; will output:

When changing a value as follows:

…and calling the query SELECT DISTINCT category FROM test ORDER BY category; again, I'll get:

But I want to get the following instead:

Is there a way to do this in SQL? Or should I do this directly in my PHP?

Answer 1

You should have 3 tables here. One will hold the the categories, the other one will hold the items and the final one will hold the relations between categories and items (it is also known as associative table ):

categories: id name
items: id name
categories_items: category_id item_id

Your query in this case will become:

SELECT id, name 
FROM categories 
ORDER BY name;

If you want to get all items from a category you could do:

SELECT id, name 
FROM items 
JOIN categories_items 
  ON items.id = categories_items.item_id
 AND categories_items.category_id = 4;

Answer 2

You should definetely normalize your tables but if you still insist on this table structure, you can try this query:

WITH CatChar(aChar, remain) AS (
   SELECT LEFT(category,1), RIGHT(category, LEN(category)-1) 
      FROM test WHERE LEN(category)>0
   UNION ALL
   SELECT LEFT(remain,1), RIGHT(remain, LEN(remain)-1) FROM CatChar
      WHERE LEN(remain)>0
)
SELECT DISTINCT aChar FROM CatChar

(Assuming your all category names are just one char length, otherwise you should reorganeze LEFT(...) part to split according to your separator)