SQL query optimization?

Question

MySQL

SELECT A.name, B.phone, %еще 20 полей%... 
FROM  `alpha` d
LEFT OUTER JOIN beta B ON A.name= B.name
WHERE A.age > 20 LIMIT 5000, 3000

This request is not fulfilled due to exceeding some hosting limits.
If you specify offset in LIMIT =0, then the data will be received. But if offset=5000, then it doesn't work anymore.
As far as I understand, the engine still shovels these 5000 lines, despite the fact that they should not be in the output.
How to optimize the query so that you can receive data with any offset ?

Answer 1

Solved the problem using subqueries.

SELECT A.name, B.phone, %еще 20 полей%... 
FROM  
  (SELECT * FROM `alpha` A.age > 20 LIMIT 5000, 5000) AS A
LEFT OUTER JOIN beta B ON A.name= B.name

Many thanks to everyone for the help.

Answer 2

EXPLAIN SELECT A.name, B.phone, %еще 20 полей%... 
FROM  `alpha` d
LEFT OUTER JOIN beta B ON A.name= B.name
WHERE A.age > 20 LIMIT 5000, 3000

Answer 3

about explain correctly speak.
And why do you need to link tables without a key? try adding indexes on a.name b.name