ORDER by multiple queries in MySql - mysql

Question

I am trying to build a chat list page where latest sent/received contact is shown at the top from one table. For this, I have a table smshistory where i store sent/received sms with numbers where one is company phone and other is client phone number
CREATE TABLE IF NOT EXISTS `smshistory` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`fromnumber` varchar(20) NOT NULL,
`tonumber` varchar(20) NOT NULL,
`sms` varchar(20) NOT NULL,
`added` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=11 ;
--
-- Dumping data for table `smshistory`
--
INSERT INTO `smshistory` (`id`, `fromnumber`, `tonumber`, `sms`, `added`) VALUES
(1, 'companynum', 'client1num', 'Hello', '2021-07-16 12:28:23'),
(2, 'companynum', 'client2num', 'Hello', '2021-07-16 12:28:23'),
(3, 'companynum', 'client3num', 'Hello', '2021-07-16 12:28:23'),
(4, 'client1num', 'companynum', 'Hi', '2021-07-16 12:28:23'),
(5, 'companynum', 'client1num', 'Hello', '2021-07-16 12:28:23'),
(6, 'client1num', 'companynum', 'Hi', '2021-07-16 12:28:23'),
(7, 'client2num', 'companynum', 'Hi', '2021-07-16 12:28:23'),
(8, 'companynum', 'client2num', 'Hello', '2021-07-16 12:28:23'),
(9, 'client3num', 'companynum', 'Hi', '2021-07-16 12:28:23');
As first message will always be from company number, so I am showing DISTINCT list with:
SELECT DISTINCT (`tonumber`) FROM `smshistory` WHERE `fromnumber` = $companynum
Which gives me list like:
client1num
client2num
client3num
Requirement:
What I require is to show the DISTINCT with order of added DESC column in a way that if a client's number is in fromnumber or tonumber, it should show at top. So, according to my table, results should be:
client3num
client2num
client1num
Fiddle is at http://sqlfiddle.com/#!9/4256d1d/1
Any idea on how to achieve that?

Answer 1

In answer to your question you can use the following query:
SELECT distinct client_num from (
SELECT CASE WHEN fromnumber = 'companynum' THEN tonumber
ELSE fromnumber END client_num
FROM smshistory ORDER BY id DESC ) as a

Answer 2

For each of the rows that contain $companynum either in fromnumber or in tonumber you must extract the client's number with a CASE expression and use GROUP BY to remove duplicates.
Finally, sort the results by the max value of added:
SELECT CASE WHEN fromnumber = $companynum THEN tonumber ELSE fromnumber END client_num
FROM smshistory
WHERE $companynum IN (fromnumber, tonumber)
GROUP BY client_num
ORDER BY MAX(added) DESC

Answer 3

In answer to the question 'How do I sort a de-normalised collection of strings (that a follow a very constrained pattern) according to the numerals contained within those strings?', here's one method...
DROP TABLE IF EXISTS x;
CREATE TABLE x
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,bad_string VARCHAR(20) NOT NULL
);
INSERT INTO x VALUES (11,'client2num'),(17,'client3num'),(21,'client1num');
SELECT REPLACE(REPLACE(bad_string,'client',''),'num','') p FROM x;
+---+
| p |
+---+
| 2 |
| 3 |
| 1 |
+---+
...which can be rewritten as follows:
SELECT * FROM x ORDER BY REPLACE(REPLACE(bad_string,'client',''),'num','') DESC;
+----+------------+
| id | bad_string |
+----+------------+
| 17 | client3num |
| 11 | client2num |
| 21 | client1num |
+----+------------+