Question

My tables: big_table

+-----------------+--------------+------+-----+---------+----------------+
| Field           | Type         | Null | Key | Default | Extra          |
+-----------------+--------------+------+-----+---------+----------------+
| id              | mediumint(7) | NO   | PRI | NULL    | auto_increment |
| title           | varchar(255) | NO   |     | NULL    |                |
| category_id     | tinyint(2)   | NO   |     | NULL    |                |
| sub_category_id | tinyint(2)   | NO   |     | NULL    |                |
| width           | smallint(5)  | NO   |     | NULL    |                |
| height          | smallint(5)  | NO   |     | NULL    |                |
| ratio_width     | smallint(5)  | NO   |     | NULL    |                |
| ratio_height    | smallint(5)  | NO   |     | NULL    |                |
| size            | int(8)       | NO   |     | NULL    |                |
| mime            | tinyint(2)   | NO   |     | NULL    |                |
| views           | mediumint(7) | NO   | MUL | NULL    |                |
| time            | int(10)      | NO   |     | NULL    |                |
| file            | varchar(255) | NO   |     | NULL    |                |
+-----------------+--------------+------+-----+---------+----------------+

small_table

+--------+--------------+------+-----+---------+-------+
| Field  | Type         | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+-------+
| id     | mediumint(7) | NO   | PRI | NULL    |       |
| width  | smallint(5)  | NO   | MUL | NULL    |       |
| height | smallint(5)  | NO   | MUL | NULL    |       |
+--------+--------------+------+-----+---------+-------+

so what’s faster (example):

   SELECT * FROM `big_table` WHERE `width` =1920 AND `height`=1080;  

or use join

 select big_table.*
 from small_table
 left join small_table small_table2
 ON (small_table.id=small_table2.id
     and `small_table`.`height` = '1080')
 left join big_table
 ON (big_table.id=small_table.id)
 where small_table.width = '1920'; 

or join’s from the same table?

select big_table.*
from big_table as big_table1
left join big_table big_table2
ON (big_table1.id=big_table2.id and  `big_table1`.`height` = '1080')
left join big_table 
ON (big_table.id=big_table1.id)
where big_table1.width = '1920';

or there is some better solution, better select’s?
(on both tables I can use indexes (width and height), but only ID is unique)

Answer 1

No join is faster that join. If you have a proper index (that is, a single index on the combination of width and height) then the simple select on big_table will be way faster.