Get partition name for specific date

[Jan Bromberger]

Hi,

for an InnoDB table historical_offers with a field
`valid_at` date NOT NULL DEFAULT '0000-00-00'
and the partitioning
PARTITION BY KEY(valid_at) PARTITIONS 92

I want to get the partition name for a specific date, so that I can truncate that partition, e.g.
ALTER TABLE historical_offers TRUNCATE PARTITION date_to_partition_name('2012-09-28')
where date_to_partition_name is what I am looking for.

I tried calculating modulo 92 the number of days since 0000-01-01 and 1970-01-01, but I got wrong numbers.

Thanks, Jan