mysql changing where clause if join exists

Question

What I want to do is join the same table and see if the field "reference_id" has a value, if it does then it should use that value to get the actual row with data and use that data for the rest of the query - where and sort clauses, otherwise use the original entries data.

Table "entries" fields:

id, text, type, reference_id, num_count

Example data:

[1, "", 0, 2, 0],
[2, "some text", 2, 0, 50],
[3, "more text", 2, 0, 60],

Should return:

row 0: "more text"
row 1: "some text"

The query looks something like this:

SELECT entries.text
FROM entries
LEFT JOIN entries as e2
     ON entries.reference_id = e2.id 
WHERE type = $type
ORDER BY num_count DESC

So the last two clauses should change from entries.type and entries.num_count to e2.type and e2.num_count if reference_id has something. How do I achieve this?

Answer 1

Please write with alias in where clause

    SELECT entries.text
FROM entries
LEFT JOIN entries as e2
     ON entries.reference_id = e2.id 
WHERE entries.type = $type
ORDER BY entries.num_count DESC

Answer 2

If I understand correctly then you just want to use the left joined table values if they exist, otherwise the main tables values.

I so something like this:-

SELECT COALESCE(e2.text, entries.text)
FROM entries
LEFT OUTER JOIN entries as e2
ON entries.reference_id = e2.id 
WHERE type = $type
ORDER BY COALESCE(e2.num_count, entries.num_count) DESC