How can I select every alternative row and display in descending order in SQL?

To fetch every alternative row, use MOD() under WHERE. Then use ORDER BY DESC to display the result in descending order −

select *from yourTableName where mod(yourColumnName,2)=1 order by yourColumnName DESC;

Let us first create a table −

mysql> create table DemoTable
(
   UniqueId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   ClientName varchar(40),
   ClientAge int
);
Query OK, 0 rows affected (1.02 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable(ClientName,ClientAge) values('Chris',34);
Query OK, 1 row affected (0.47 sec)
mysql> insert into DemoTable(ClientName,ClientAge) values('Tom',45);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable(ClientName,ClientAge) values('Sam',36);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable(ClientName,ClientAge) values('Carol',42);
Query OK, 1 row affected (0.25 sec)
mysql> insert into DemoTable(ClientName,ClientAge) values('David',38);
Query OK, 1 row affected (0.12 sec)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

+----------+------------+-----------+
| UniqueId | ClientName | ClientAge |
+----------+------------+-----------+
|        1 | Chris      |        34 |
|        2 | Tom        |        45 |
|        3 | Sam        |        36 |
|        4 | Carol      |        42 |
|        5 | David      |        38 |
+----------+------------+-----------+
5 rows in set (0.00 sec)

Let us now select every alternative row and display in descending order −

mysql> select *from DemoTable where mod(UniqueId,2)=1 order by UniqueId DESC;

This will produce the following output −

+----------+------------+-----------+
| UniqueId | ClientName | ClientAge |
+----------+------------+-----------+
|        5 | David      |        38 |
|        3 | Sam        |        36 |
|        1 | Chris      |        34 |
+----------+------------+-----------+
3 rows in set (0.00 sec)