MySQL sort differently in "batch" - mysql

Question

Below is the standard query that sort weight in descending order.
SELECT * FROM article ORDER BY weight DESC LIMIT 0, 4
+-------------+--------+
| title | weight |
+-------------+--------+
| B | 2 |
| E | 2 |
| Y | 2 |
| A | 1 |
| C | 1 |
| D | 1 |
| F | 1 |
| G | 1 |
| X | 1 |
| Z | 1 |
| I | 1 |
| G | 1 |
+-------------+--------+
However, I wish to sort it differently as following based on the weight value.
+-------------+--------+
| title | weight |
+-------------+--------+
| B | 2 |
| A | 1 |
| C | 1 |
| D | 1 |
| E | 2 |
| F | 1 |
| G | 1 |
| X | 1 |
| Y | 2 |
| Z | 1 |
| I | 1 |
| G | 1 |
+-------------+--------+
The record with weight value 2 only selected once and sorted at the top. Then followed by records with weight value 1.

Answer 1

Using the approach like in these answers:
ROW_NUMBER() in MySQL
MSSQL Row_Number() over(order by) in MySql
you could obtain row numbers, separately, for rows with weight value of 2 and for rows with any other weight value, then use the resulting numbers for sorting.
Before I continue, please note that, even though the official documentation admits that
You might get the results you expect,
it also advises that,
As a general rule, you should never assign a value to a user variable and read the value within the same statement.
(By the same statement it means a statement other than SET.)
Below is a way of getting the expected order if the results are as they are expected.
SET #row2 = -1;
SET #row_other = -1;
SELECT
title, weight
FROM (
SELECT
title, weight,
#row2 := #row2 + CASE weight WHEN 2 THEN 1 ELSE 0 END AS weight2_row,
#row_other := #row_other + CASE weight WHEN 2 THEN 0 ELSE 1 END AS other_weight_row
FROM article
) s
ORDER BY
CASE weight WHEN 2 THEN #row2 ELSE #row_other DIV 3 END,
weight = 2 DESC
The specific order for non-Weight=2 rows is undefined, just like it is in your question.

Answer 2

Taking the same precautions that Andriy states, you can also use this:
SELECT title, weight
FROM
( SELECT title, weight
, #rownumber2 := #rownumber2 + 3 AS rn
FROM article
, ( SELECT #rownumber2 := 1 ) AS dummy
WHERE weight = 2
ORDER BY title --- optional, configure it for the
--- ordering of rows with weight = 2
UNION ALL
SELECT title, weight
, #rownumber1 := #rownumber1 + 1 AS rn
FROM article
, ( SELECT #rownumber1 := 3 ) AS dummy
WHERE weight = 1
ORDER BY title DESC --- optional, configure it for the
--- ordering of rows with weight = 1
) AS insaneOrdering
ORDER BY rn
, weight DESC ;