How to keep the first X rows and delete table rows

Question

I have a large table with millions of records in MySQL incident_archive and I want to sort the rows by the created column and keep the first X rows and delete the rest OK, what's the most efficient way.

So far I've come up with this solution in Python:

def do_delete_archive(rowsToKeep):

    if rowsToKeep > 0:
        db_name = find_environment_value('DB_NAME', False, "dbname")
        db_host = find_environment_value('DB_HOST', False, "host")
        db_user = find_environment_value('DB_USER', False, "username")
        db_pass = find_environment_value('DB_PASS', False, "password")
        db = MySQLdb.connect(host=db_host,user=db_user,passwd=db_pass,db=db_name)
        cursor = db.cursor()            
        
        sql = f"""DELETE FROM `incident_archive` 
                    WHERE incident_id NOT IN 
                    ( SELECT incident_id FROM 
                    ( SELECT incident_id FROM `incident_archive` ORDER BY created DESC LIMIT {rowsToKeep}) foo) LIMIT 10000;"""
        
        try:
            rowcount = rowsToKeep+ 1
            while rowcount > rowsToKeep:
                cursor.execute(sql)
                db.commit()
                rowcount = cursor.rowcount
                print(f"--- Affected Rows: {rowcount} ---")

        except:
            db.rollback()

The problem I have here is that this method will not work if the value of rowsToKeep is greater than or equal to 10000, what is a better way of doing this process?

**Note: The rowsToKeep value is dynamic, which means it can change.

Answer 1

I came up with the following solution:

Note: Threshold is the variable containing the maximum number of records we wish to keep at 1000 in our example

sqlCreate = f"""CREATE TABLE new_incident_archive LIKE incident_archive;"""
print(f"Running query is: {sqlCreate}")
cursor.execute(sqlCreate)
print(f"Done with: {sqlCreate}")

sqlInsert = f"""INSERT INTO new_incident_archive SELECT * FROM `incident_archive` ORDER BY created DESC LIMIT {threshold}"""
print(f"Running query is: {sqlInsert}")
cursor.execute(sqlInsert)
db.commit()
print(f"Done with: {sqlInsert}")

sqlDrop = f"""DROP TABLE incident_archive"""
print(f"Running query is: {sqlDrop}")
cursor.execute(sqlDrop)
print(f"Done with: {sqlDrop}")

sqlRename = f"""RENAME TABLE `new_incident_archive` TO `incident_archive`;"""
print(f"Running query is: {sqlRename}")
cursor.execute(sqlRename)
print(f"Done with: {sqlRename}")