How can I sort by multiple columns but not by value?

问题

Question title might be a bit vague, so feel free to change it into something that makes more sense, I just couldn't find the right words.

So here is my problem:

In my table there are 2 important columns

• date_added (a datetime value)
• special_price (numeric)

special_price is either NULL or a numeric value depending on what the special price is.

I'll describe the way I want to order my result now:

First I want to see all the items with no special_price (NULL) ordered by date (newest first), Then I want to see the items that do have a special_price (so anything other than NULL) ordered by date.

At first I tried this:

SELECT * FROM products ORDER BY special_price, date_added DESC

This worked great for the first part where all the special_price values where NULL, but when it started with the the items that did have a special_price ordered on the value that was in the special_price column. This makes sense of course because in the query I wanted to order by special_price first.

So how can I let the query ignore the value of special_price and just see whether it's NULL or not? So I get all NULL's ordered by date and then I get all the NOT NULL's ordered by date.

回答1:

ORDER BY IF( ISNULL( special_price ), 0, 1 ), date_added DESC

回答2:

I'd use

SELECT *, IF(special_price IS NULL, 0, 1) AS orderer FROM products ORDER BY orderer, date_added DESC

that works fine for what you want to accomplish

来源：https://stackoverflow.com/questions/6857110/how-can-i-sort-by-multiple-columns-but-not-by-value