MySql conditional order by

Question

I have this table (simplified):

CREATE TABLE `my_table` (
  `id` INT NOT NULL AUTO_INCREMENT ,
  `item_name` VARCHAR(45) NULL ,
  `price` DECIMAL(10,0) NULL ,
  PRIMARY KEY (`id`) 
)

I need to select all items from the table, ordered this way:

1. items with price > 0.00 first, ordered by price ASC
2. items with price = 0.00 last, ordered by id

I tried this:

SELECT * 
FROM my_table 
WHERE 1  
ORDER BY 
  CASE price WHEN !0.00 THEN price 
   ELSE id
  END 
ASC

And I get results like

item_name	price
foo	150,00
bar	0,00
baz	500,00
hum	0,00

How do I build the query to have

item_name	price
foo	150,00
baz	500,00
bar	0,00
hum	0,00

Thank you for your time

Solution 1

This will do the trick..

 SELECT * 
    FROM my_table 
    WHERE 1  
    ORDER BY 
      CASE price WHEN 0 THEN 1
       ELSE -1
      END ASC, price asc, id asc

Solution 2

You can also use the following:

SELECT * 
FROM my_table 
WHERE 1  
ORDER BY price=0, price, id;

The part 'price=0' will be 1 for items with zero price, 0 for items with non-zero price. As the default sort order is ASC, non-zero items are now placed first.

The next bit of the order-by clause means that non-zero items are then sorted by price (again ascending). If any items with non-zero price have the same price, they will be further sorted by id, but we don't care about that.

The last part is only there for items where price=0. As all these items do have the same price, the effect is to sort all the zero-priced items by id.

Comments

[ecstrim]

Wonderfull, thank you very much! One question, the 1 and -1 from THEN and ELSE what do they mean?

[Matthew Flaschen]

It means when price is 0, assign 1 for the sort, otherwise assign -1. Any two values would work, as long as the THEN value is greater than the ELSE value.

[Gabriele Petrioli]

What @Matthew mentioned. We give a value to each row (of 1 or -1) according to its price (0 or greater) and then sort by that value. So the rows with -1 will be first (those with a price >0) and those with 1 will be last (those with price = 0).