Question

Let’s say I want to retrieve 100 records from a table called messages, and I want to obtain them the following way:

1st message
100th message
2nd message
99th message
3rd message
98th message
(...)

Is there any way to do this efficiently? What would be the appropriate query?
Or should I make a query to select the first 50, a query to select the last 50 and then merge the results?

Answer 1

Try if your ID is a sequence of numbers:

First

SET @half = (SELECT MAX(id) FROM messages)/2;

Then

SELECT * FROM `messages` ORDER BY (IF(id<@half,@half*2-id,id-1)) DESC,id ASC;