php - Deleting all but the last 30 rows in database table with MySQL -


i have simple question. how can delete last 30 rows in database table? example, take following query:

delete comments got='$user_id'

what else need in order keep last 30 rows?

this comments table looks like:

enter image description here

if version if mysql supports limits within sub-queries, can use sub-query selects 30 recent rows. then, can delete except rows found in sub-query.

delete comments got='$user_id'   , got not in     (select got      comments      order timestamp desc limit 30)

if mysql version not support limits within sub-queries, you'll need split 2 separate queries:

query 1

select got comments got='$user_id' order timestamp desc limit 30

the results of query 1 should stored in single string variable (using format 1,2,3...) , passed query 2. (the explode , implode functions may come in handy when formatting string.)

query 2

delete comments got='$user_id'   , got not in ($formatted_result_from_query_1)

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