The mysqlnd replication and load balancing plugin (mysqlnd_ms) adds easy to use MySQL replication support to all PHP MySQL extensions that use mysqlnd.

via PHP: Introduction – Manual.

Whilst a truncate table operation is underway a lock mutex around the table is created to ensure data consistency; if using innodb file per table the physical .ibd file must be removed which is a painfully slow operation under ext3.

via A quicker drop table within MySQL:

select make_set(255,’bit0′,’bit1′,’bit2′,’bit3′,’bit4′,’bit5′,’bit6′,’bit7′);

select (1,2,3)=(1,2,3);

Based on a similar concept, combined with string walking, I now present a query which selects top-n records for each group, ordered by some condition. It will require no subqueries. It executes faster than its more conventional alternatives.

via SQL: selecting top N records per group | code.openark.org.


SELECT * FROM a LEFT JOIN b ON a.id=b.id
UNION ALL
SELECT * FROM a RIGHT JOIN b ON a.id=b.id WHERE a.id IS NULL;

+------+------+------+------+
| id   | name | id   | name |
+------+------+------+------+
|    1 | a    | NULL | NULL |
|    2 | b    |    2 | b    |
|    1 | a    | NULL | NULL |
| NULL | NULL |    3 | c    |
+------+------+------+------+

Why doesn’t MySQL implement FULL OUTER JOIN syntax for this? We don’t know.

via Common Queries Tree.

Then the binlog before ‘mydb-bin.0023′ will be deleted.

You may also do this:

PURGE MASTER LOGS BEFORE ’2008-06-13 08:00:00′;