Question

How to get result on PHP:

• NU61 – sun – 2011
• KE2I – ball – 2000
• B8WO – point – 2008

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table_first SELECT id, order, date FROM table_first ORDER BY orders DESC
return id, date

 id   | orders  | date
------+---------+------
 KE2I | 2       | 2000
 B8WO | 5       | 2008
 NU61 | 1       | 2011

table_second SELECT key FROM table_second WHERE id=(id from table_first) get key to reach content from table_third

 id   | key
------+-----------------
 KE2I | .b
 B8WO | .p
 NU61 | .s

table_third SELECT content FROM table_third WHERE id=(key from table_second) return content

 id   | content
------+-----------------
 .b   | ball
 .p   | point
 .s   | sun

Answer 1

SELECT `table_first`.`id`,
       `table_third`.`content`,
       `table_first`.`date`
FROM `table_first`
LEFT JOIN `table_second` USING(`id`)
LEFT JOIN `table_third` ON `table_third`.`id`=`table_second`.`key`

Performance will not be a concern as long as you have indices on:

`table_first`.`id`
`table_second`.`id`
`table_second`.`key`
`table_third`.`id`