I wish to return area name from the database table where id = 4. Which totally simpler for MYSQL to process.

SELECT name, id FROM table WHERE id = 4

or

SELECT name FROM table WHERE id = 4

I guess I am asking whether it's sound practice to place the area in the WHERE statement in SELECT too even when I will not give it back in php.

SELECT name, id FROM table WHERE id = 4

would also provide the id within the derive from mysql also it will make hardly any impact on the information because it is merely a numeral however should you do that in which you were choosing another thing for example SELECT name, id FROM table WHERE name = "ron" would certainly a poor practice weight loss information is being moved in the database server as you know the title "ron" and as it is not unique it might have several rows.

mysql> explain select id,name from admin_users where id = 1;
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref   | rows | Extra |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
|  1 | SIMPLE      | admin_users | const | PRIMARY       | PRIMARY | 4       | const |    1 |       |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
1 row in set (0.00 sec)

mysql> explain select name from admin_users where id = 1;
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref   | rows | Extra |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
|  1 | SIMPLE      | admin_users | const | PRIMARY       | PRIMARY | 4       | const |    1 |       |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
1 row in set (0.00 sec)

in comparison to

mysql> explain select id,name from admin_users where name = 'ron';
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref   | rows | Extra |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
|  1 | SIMPLE      | admin_users | const | PRIMARY       | PRIMARY | 4       | const |    1 |       |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
123 row in set (0.11 sec)

mysql> explain select name from admin_users where name = 'ron';
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
| id | select_type | table       | type  | possible_keys | key     | key_len | ref   | rows | Extra |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
|  1 | SIMPLE      | admin_users | const | PRIMARY       | PRIMARY | 4       | const |    1 |       |
+----+-------------+-------------+-------+---------------+---------+---------+-------+------+-------+
123 row in set (0.05 sec)

If you do not require the id came back, don't include it. If you want it, include it.

No, that isn't sound practice. SELECT precisely individuals fields that you simply need.