Sort result with empty strings first - mysql

Question

I have this locations table:
+----+-----------+------------+----------+
| id | country | state | city |
+----+-----------+------------+----------+
| 1 | US | Georgia | Atlanta |
| 2 | US | California | |
| 3 | US | | |
| 4 | Canada | Ontario | |
| 5 | Canada | Manitoba | Winnipeg |
| 6 | Canada | | |
I want to create a query but could not build my ORDER BY properly. This is the result that I want:
+----+-----------+------------+----------+
| id | country | state | city |
+----+-----------+------------+----------+
| 6 | Canada | | |
| 3 | US | | |
| 4 | Canada | Ontario | |
| 2 | US | California | |
| 5 | Canada | Manitoba | Winnipeg |
| 1 | US | Georgia | Atlanta |
Basically, this is the priority that I want to follow:
Country listing. Alphabetical order.
State listing. Alphabetical order.
City listing. Alphabetical order.
This query does not seem to account for empty columns (I am not using NULLs in my locations table):
SELECT * FROM locations
ORDER BY
country,state,city

Answer 1

Try this ORDER BY clause:
SELECT *
FROM locations
ORDER BY
CASE WHEN state = '' AND city = '' THEN 0
WHEN city = '' THEN 1
ELSE 2 END,
country,
state,
city;
This sorting logic places first those records which are missing both state and city. Next follows records missing city only, followed last by records having non empty data for all three fields.

Answer 2

For versions pre 8.0...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id SERIAL PRIMARY KEY
,country VARCHAR(20) NOT NULL
,state VARCHAR(20) NULL
,city VARCHAR(20) NULL
);
INSERT INTO my_table VALUES
(1,'US','Georgia','Atlanta'),
(2,'US','California',NULL),
(3,'US',NULL,NULL),
(4,'Canada','Ontario',NULL),
(5,'Canada','Manitoba','Winnipeg'),
(6,'Canada',NULL,NULL);
SELECT id
, country
, state
, city
FROM
( SELECT x.*
, CASE WHEN #prev=country THEN #i:=#i+1 ELSE #i:=1 END i
, #prev:=country
FROM my_table x
, (SELECT #prev:=null,#i:=0) vars
ORDER
BY country
, city
, state
) a
ORDER
BY i
, country;
+----+---------+------------+----------+
| id | country | state | city |
+----+---------+------------+----------+
| 6 | Canada | NULL | NULL |
| 3 | US | NULL | NULL |
| 4 | Canada | Ontario | NULL |
| 2 | US | California | NULL |
| 5 | Canada | Manitoba | Winnipeg |
| 1 | US | Georgia | Atlanta |
+----+---------+------------+----------+

Answer 3

select *
from locations
order by
state <> '',
city <> '',
country,
state,
city
db-fiddle
Note that in MySQL a boolean expression returns 0 (for FALSE) or 1 (for TRUE). That means for an empty state string state <> '' will return 0 and thus ordered first.