mysql - SQL selecting X random rows within top Y after ordering -

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using mysql, wish select

1) 5 random rows among top 20 rows after ordering "price" column

2) 15 random rows among 30 next results (rows 21-50) after ordering "price" column

what best way achieve performance-wise sql? please note table contains around 1,000,000 rows.

the final purpose update column (set status=1) these randomly selected rows.

use nested selects - should quite fast in situation

select *  ( select .... table  order price limit x, y ) order random

replace x , y appropriate values

note depending on particular rdbms "order random" , "limit" clauses may differ! mysql way.

the important thing server inner select first, return 20-30 rows (depending on limit clause) , can sort in random order in outer select. if price column indexed fast enough


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